Charging method, charging equipment, and integrated circuit

ABSTRACT

When a secondary battery such as a lithium ion battery, etc. requiring constant-voltage charging is charged, the battery voltage and charging current of the secondary battery are detected under a specified state, and in accord with the detected state, a voltage at which charging is carried out, the charging time or charging stop period thereof, or connecting condition of the charging circuit etc. are controlled in order to favorably charge the secondary battery to a full-charge or to a nearly full-charged state, thereby effectively preventing deterioration of characteristics of the secondary battery.

TECHNICAL FIELD

The present invention relates to a charging method and chargingequipment for secondary batteries and an integrated circuit used for itscharging control, and more particularly to a charging method andcharging equipment suitable for applying to secondary batteries whichrequire constant-voltage charging such as lithium ion batteries or thelike and an integrated circuit used for its charging control.

BACKGROUND ART

Conventionally, for secondary batteries which are able to be charged andrequire constant-voltage charging, lithium ion batteries are developed.This lithium ion battery is charged with the characteristics shown, forexample, in FIG. 1. FIG. 1 is a characteristic diagram of chargingcurrent/voltage vs. elapsed time of a general lithium ion battery, inwhich charging is carried out with a charging current I set as aconstant current from the initiation of charging until the batteryvoltage reaches a specified potential. Carrying out thisconstant-current charging increases a battery voltage V and when itexceeds a specified value, charging is changed over to constant-voltagecharging. In this event, for example, voltage V₁ corresponding tobattery voltage when the lithium ion battery is fully charged (that is,100% charged) is supplied. Carrying out this constant-voltage chargingcharges the lithium ion battery, causes the battery voltage to rise tovoltage V₁, but as this charging takes place, the charging current Idecreases. Now, when this charging current I decreases to a specifiedvalue, it is judged that the lithium ion battery is 100% charged (orcharged nearly to 100%), and supply of charging current is stopped.

Charging in this way allows the lithium ion battery to be efficientlycharged to 100%.

Now, the lithium ion battery charged to 100% in this way may sometimeshave the characteristics deteriorated by the charging conditionthereafter. That is, if the voltage V₁ corresponding to battery voltagewhen the lithium ion battery is fully charged is constantly applied tothe 100% charged lithium ion battery from the charging equipment ascharging voltage and small-power charging is repeatedly carried out, thecharging condition can be maintained to nearly 100% condition even whenthere is self-discharge. However, when such nearly 100% conditioncontinues, the lithium ion battery becomes characteristics which tendsto gradually reduce the chargeable capacity, and eventually deterioratesthe characteristics as a secondary battery.

In order to prevent characteristics deterioration due to thecontinuation of the 100% charged condition, for example, stoppingcharging at about 90% of the charging capacity is assumed, but thisresults in inconvenience that the capacity prepared as a secondarybattery is not effectively utilized.

When temperature of the battery itself rises, the lithium ion batteryhas a disadvantage that the chargeable capacity decreases and batterycharacteristics rapidly deteriorate, and it also has a disadvantage thatit is not preferable to be charged to the full charging level with thebattery temperature increased at the time of charging under the sameconditions as those free of temperature rise.

As described above, it is when there remains scarcely charged voltage inthe lithium ion battery to carry out constant-current charging at firstand then change over to constant-voltage charging to charge the battery,and when any voltage remains in the battery, it is necessary to carryout constant-voltage charging with the charging current reduced, therebypreventing deterioration of characteristics as a secondary batteryresulting from rapid charging by large current.

Consequently, before charging is started, the condition of the batteryto be charged must be detected and the remaining voltage must bedetected. In order to detect this remaining voltage, charging is carriedout with a small current called pre-charging at the start of charging,the battery voltage, etc. at that time is detected, and the remainingvoltage of the battery is detected.

FIG. 2 shows one example of a circuit configuration of a conventionalcharging equipment which can carry out the pre-charging, in which to oneend on the secondary side (primary side is omitted) of a switchingtransformer 1 that composes the switching power supply, the anode ofdiode 2 is connected, and the cathode of this diode 2 and the other endon the secondary side of a transformer 1 are connected with a capacitor3, and direct current power supply of a specified voltage is obtained byrectification by diode 2 and smoothing by capacitor 3.

The cathode of diode 2 is connected to one end (positive electrode) of asecondary battery (lithium ion battery) 4 loaded to this chargingequipment via an opening and closing switch SW1, and the other end(negative electrode) of this secondary battery 4 is connected to theother end on the secondary side of the switching transformer 1. Inparallel to the opening and closing switch SW1, a series circuitcomprising an opening and closing switch SW2 and a resistor 5 isconnected.

In this event, opening and closing of switches SW1 and SW2 arecontrolled by a control circuit 6. This control circuit 6 is connectedin such a manner that the power supply is fed from the secondary side ofthe switching transformer 1 and is operated by this power supply. Andthis control circuit is designed to detect the condition of thesecondary battery 4 by some method not illustrated (for example,detection of battery voltage).

To explain the control by the control circuit 6, at the start ofcharging, the switch SW2 is held closed, while the switch SW1 is heldopen. Keeping the switches in this condition allows the power supply tobe fed from the secondary side of switching transformer 1 with theresistor 5 connected to the secondary battery 4 in series, reduces thecharging current to be fed to the secondary battery 4 as much as theloss caused by this resistor 5, and allows pre-charging by small currentto take place. And under this pre-charging condition, the batterycondition such as battery voltage of the secondary battery 4 or the likeis detected by the control circuit 6, and if the detected condition isjudged to be the condition with little remaining voltage that allowsrapid charging, switch SW1 is held closed, switch SW2 is held open,charging current is supplied to the secondary battery 4 with theresistor 5 in the condition free of loss, and rapid charging by largecurrent is begun.

Now, FIG. 3 shows the charging characteristics when switch SW1 is turnedon and those when switch SW2 is turned on, indicating that comparativelylarge current is allowed to flow at a given voltage as chargingcharacteristics when switch SW1 is turned on. The chargingcharacteristics when switch SW2 is turned on are such that the currentvalue is suppressed to a small value.

In this way, configuring to provide a plurality of paths foraccommodating the charging current and to vary the charging current tocarry out pre-charging results in complicated configuration of thecharging equipment as much and constitutes an inconvenience.

As a configuration of another charging equipment for enablingconventional pre-charging, there is one with the circuit configurationshown in FIG. 4. In the case of this circuit, the cathode of diode 2 isconnected to one end (positive electrode) of the secondary battery 4(lithium ion battery) mounted to this charging equipment via anopening/closing closing switch SW3, and the other end (negativeelectrode) of this secondary battery 4 is connected to the other end onthe secondary side of the switching transformer 1.

And opening and closing of the switch SW3 are controlled by a controlcircuit 7. This control circuit 7 is connected in such a manner that thepower supply is fed from the secondary side of the switchingtransformer 1. And this control circuit is designed to detect thecondition of the secondary battery 4 by some method not illustrated (forexample, detection of battery voltage), and opening and closing ofswitch SW3 are controlled based on the detected condition.

Now, to explain the control condition of switch SW3, in carrying outordinary charging (rapid charging, etc.), switch SW3 is continuouslyheld closed, and in carrying out pre-charging with small current,opening and closing of switch SW3 are repeatedly carried out. That is,for example, as shown in FIG. 5, when precharging is carried out at thestart of charging, ON/OFF of switch SW3 are repeated to intermittentlysupply a specified current value I to the secondary battery 4, andaverage charging current is lowered, bringing about the conditions inwhich pre-charging Pre is able to be carried out by small current. Whenprecharging is switched to ordinary charging, switch SW3 is continuouslyheld closed, and charging by the specified current value I iscontinuously carried out.

Pre-charging by intermittently opening and closing this switch in thisway enables both ordinary charging and pre-charging only by installingone switch, but at the time of pre-charging by ON/OFF of this switch,the peak current when opening and closing of the switch are changed overis transmitted to the control circuit 7, and there is a high possibilityto adversely affect operation of the control circuit 7. Consequently,pre-charging by repeating ON/OFF of the switch in this way is notpreferable.

Another problem is an error in detection of battery voltage in thebattery charger, and there is a case in which the error deteriorates thebattery characteristics.

That is, FIG. 6 shows one example of the charging control condition whenthe conventional lithium ion battery is 100% charged. For example,suppose that a lithium ion battery with voltage V₁ when fully charged ischarged and the battery voltage of this battery reaches V₁ at a certaintiming t₁. In this event, this lithium ion battery is judged to be fullycharged and supply of charging current is stopped. Stopping chargingcauses the lithium ion battery to gradually reduce battery voltage dueto self discharge or discharge to the load circuit.

Now, the charging circuit is set to restart charging when the batteryvoltage reaches a predetermined voltage V₂. Suppose that the chargingcircuit detects this battery voltage V₂ at timing t₂, then, charging isrestarted at this timing t₂, and the battery voltage rises again asshown with characteristic Vx, achieving the fully charged condition.

By setting in this way, the battery voltage is able to be held to thevoltage close to full charging. Now the lithium ion battery isconstantly charged nearly 100% by bringing the voltage V₂ to restartcharging to a voltage value extremely close to the battery voltage V₁when fully charged, but since achieving this state acceleratesdeterioration of the battery, voltage V₂ to restart charging shall beset to the voltage slightly reduced from the battery voltage V₁ whenfully charged to allow the remaining battery voltage to vary in acertain range, thereby preventing deterioration of the battery.

However, in general, in the voltage detection circuit with comparativelysimple configuration built into this kind of battery charger, it isdifficult to constantly accurately detect voltage V₁₂, and an error ΔVis generated in the detection value of the voltage. Now, as shown inFIG. 6, if a voltage higher than actual setting by the error ΔV isjudged to be the voltage V₁ (timing t₂ '), the battery returns to thefully charged condition more quickly than the originally set condition(condition by characteristic Vx) as in the case of the characteristic Vyshown with broken line, and deterioration of the battery characteristicsis accelerated.

In addition, when the secondary battery is charged to full charge andcharging is stopped, depending on the condition on the battery chargerside, there is a case in which discharge current is generated from thesecondary battery to the battery charger side, and in such event,charging of the secondary battery is restarted in a short time,shortening the frequency to carry out charging.

DISCLOSURE OF THE INVENTION

In view of the foregoing problems, it is the first object of theinvention to effectively utilize the battery capacity withoutdeteriorating the battery.

The second object is to detect the battery condition in a simpleconstruction and accurately upon charging.

The third object is to effectively charge the battery withoutdeteriorating the battery even if there is any detection error in thebattery condition.

The fourth object is to prevent wasteful discharge from the secondarybattery in the fully charged condition of the secondary battery.

The first invention is a charging method to change over the voltageapplied to the secondary battery to the second voltage lower than thefirst voltage when charging current is detected during charging byapplying the first voltage to the secondary battery and the firstcharging current corresponding to the nearly fully charged condition ofthe said secondary battery is detected in the charging method forcharging the secondary battery which is charged by constant-voltagecharging, as well as to change over the voltage application to that ofthe first voltage when the current exceeding the second charging currentcorresponding to the specified remaining battery voltage is detected,with the second voltage applied to the secondary battery. By thischarging method, only when the remaining battery voltage lowers to thespecified value, the battery is charged to the fully charged conditionby the first voltage. Consequently, after the battery is once charged tothe fully charged condition, charging to full charge is repeated everytime the battery lowers to the specified remaining battery voltage, andthe secondary battery condition can be constantly maintained to thenearly fully charged condition, and at the same time, because the secondvoltage lower than the first voltage is applied to the battery exceptwhen charging to this full charge is carried out, the secondary batteryis not continuously brought to the fully charged condition, anddeterioration in secondary battery performance caused by continued fullycharged condition can be prevented.

The second invention uses the same current value for the said secondcharging current and the said first charging current in the chargingmethod according to the first invention. According to this chargingmethod, charging condition can be successfully controlled.

The third invention is a charging method according to the firstinvention designed to detect temperature inside or in the vicinity ofthe said secondary battery, and to change over the application of thesaid second voltage to the application of the third voltage of thepotential across the said first and the second voltages in place ofchanging it over to the said first voltage when the detected temperatureexceeds a specified temperature. According to this charging method, itis possible to suppress deterioration of secondary battery performancecaused by temperature rise.

The fourth invention is a charging method according to the thirdinvention designed to continuously change the said third voltage inaccordance with the temperature detected as above. According to thischarging method, charging control corresponding to temperature isfavorably carried out.

The fifth invention is a charging method to detect the battery voltageof the said secondary battery while charging the said secondary batteryby applying the first voltage according to the charging method of thesecondary battery where charging takes place by constant-voltagecharging, to change over the voltage applied to the said secondarybattery to the second voltage lower than the said first voltage when aspecified voltage corresponding to the nearly full-charge state of thesaid secondary battery is detected, and at the same time, to change overto application of the said first voltage when a specified chargingcurrent is detected with this second voltage applied to the secondarybattery. According to this charging method, the battery is charged tonearly full-charge state only when the remaining battery voltage lowersto a specified value. Consequently, once after it is charged to thefull-charge state, charging to the full-charge is repeatedly carried outevery time the battery remaining voltage lowers to a specified value,thereby maintaining the secondary battery condition constantly to nearlyfull-charge state, and at the same time, because except when thischarging to the full-charge is carried out, the secondary voltage lowerthan the first voltage is applied, the secondary battery is notcontinuously brought to the full-charge state and thereby deteriorationof the secondary battery performance caused by continuation of thefull-charge state can be prevented.

The sixth invention is a charging method according to the fifthinvention wherein the application of the said second voltage is changedover to the application of the third voltage of the potential betweenthe said first and the second voltages in place of changing it over toapplication of the said first voltage when temperature inside or in thevicinity of the said secondary battery is detected and the detectedtemperature is a specified temperature or higher. According to thischarging method, it is possible to favorably control the charging state.

The seventh invention is a charging method according to the sixthinvention designed to continuously change the said third voltage inaccord with the temperature detected as above. According to thischarging method, it is possible to favorably control charging in accordwith the temperature.

The eighth invention is a charging method designed to detect thepotential across one end and the other end of a switching means forcontrolling start and stop of supply of the charging power supply to thesaid secondary battery or the potential across one end and the other endof the said secondary battery with low-voltage charging power supply fedto the said secondary battery in the charging method for charging thesecondary battery which requires constant-current charging at the startof charging, to turn on the said switching means based on this detectedpotential, and at the same time to start charging to the secondarybattery with the charging power supply to be fed to the said secondarybattery designated as a specified potential. According to this chargingmethod, it is possible to control the switching means and to detect thesecondary battery condition based on the detection of the potentialacross one end and the other end of this switching means or thepotential across one end and the other end of the secondary battery,thereby enabling accurate detection of the secondary battery conditionas in the case of the conventional pre-charging. Consequently, it ispossible to accurately detect the secondary battery condition withoutproviding a charging circuit specialized for pre-charging and tosimplify the circuit configuration of the charging equipment.

The ninth invention is a charging method according to the eighthinvention designed to use a field effect transistor as the saidswitching means, to increase the impedance across one end and the otherend of this field effect transistor, and to detect the said potential.According to this charging method, only carrying out the impedancecontrol of the field effect transistor, it is possible to easily detectthe secondary battery condition, and at the same time to reduce the lossof the field effect transistor even when the battery voltage of thesecondary battery is low or shorted.

The tenth invention is a charging method according to the eighthinvention designed to keep the potential of the said charging powersupply when the said potential is detected to the value in the vicinityof the lowest required voltage for controlling the said switching means.According to this charging method, it is possible to detect thesecondary battery condition with the lowest voltage charging powersupply fed to the secondary battery, and to detect the electricalcondition of the secondary battery with the minimum load applied to thesecondary battery and the circuit, as well as to detect the secondarybattery electrical state under the favorable condition.

The 11th invention is a charging method according to the eighthinvention designed to raise the potential of the said charging powersupply in accord with an increase of the potential across one end andthe other end of the said secondary battery after the start of the saidcharging. According to this charging method, it is possible to nearlyuniformly hold the electric power applied to the switching means, and itis also possible to hold the switching means to a favorable condition.

The 12th invention is a charging method according to the eighthinvention designed to change and increase the potential of the saidcharging power supply in a plurality of stages in accord with anincrease of the potential across one end and the other end of thesecondary battery after the said charging begins. According to thischarging method, it is possible to nearly uniformly keep the electricpower applied to the switching means, and it is also possible to keepthe switching means to the favorable condition. In this case, sincevoltage is allowed to be varied in a plurality of stages, a simplecontrol is only required for the voltage circuit.

The 13th invention is a charging method according to the eighthinvention designed to lower the potential of the said charging powersupply, when the said potential is detected, to the voltage below theminimum required one for controlling the said switching means, and atthe same time to accumulate this charging power supply by acharge-storage means, thereby securing the potential required forcarrying out the corresponding control by the said switching means.According to this charging method, as long as electric charge isaccumulated in the charge-storage means, it is possible to keep thevoltage of the charging power supply to be fed to the secondary batterywhen the voltage is detected with a detection means to the voltage lowerthan the one which can control the switching means, enabling thedetection of the secondary battery condition more favorably with lowervoltage applied.

The 14th invention is a charging method for enabling the restart ofcharging of the secondary battery after a specified time passes fromthis detection when the said secondary battery is detected to achieve aspecified electrical state after charging is stopped when the nearlyfull-charge state is detected in a charging method for charging thesecondary battery which is carried out by constant-voltage charging.According to this charging method, it is possible to designate the timeto restart charging once it comes in the full-charge state (or nearlyfull-charge state) to the time in which a specified time is added to thetime for a battery to reach a specified electrical condition, and evenif any error exists in the detected battery condition, it is possible tosecure a certain time for returning to the full-charge condition, and itis thereby possible to prevent deterioration of characteristics of thesecondary battery caused by continuation of the full-charge conditions.

The 15th invention is a charging method according to the 14th inventiondesigned to detect the said specified electrical condition and to detectthat the battery voltage of the said secondary battery lowers by aspecified value from the voltage with the said charging voltage set as astandard. According to this charging method, it is possible to exactlydetect the decrease of battery voltage with the charging voltage as astandard, and to accurately control the condition of the secondarybattery.

The 16th invention is a charging method according to the 14th inventiondesigned to detect the said specified electrical condition, and todetect that the battery voltage becomes a specified voltage from thevoltage value with the grounding potential of the said secondary batteryset as a standard. According to this charging method, it is possible toproperly control the secondary battery condition by comparatively simplevoltage detection.

The 17th invention is a charging method according to the 14th inventiondesigned to detect that the charging current when a specified voltage isapplied to the said secondary battery becomes a specified value asdetection of the said required electrical condition. According to thischarging method, it is possible to properly control the chargingcondition of the secondary battery based on the detection of the currentvalue.

The 18th invention is a charging method according to the 17th inventionwherein the said required voltage is lower than the charging voltage ofthe said constant voltage. According to this invention, it is possibleto detect the secondary battery condition by the voltage lower than thecharging voltage, and to properly detect the battery condition with aload applied to the secondary battery reduced.

The 19th invention is a charging method for charging the secondarybattery with the constant voltage charging voltage, which is designed todetect the electrical condition of the said secondary battery every timea specified time passes from the time when the nearly full-charge of thesecondary battery is detected to the time when charging is stopped, andto restart charging when this detected electrical condition is aspecified condition. According to this charging method, it is possibleto keep the time open at least for the specified period from the timewhen charging is stopped once full-charge condition is attained to thetime when charging is restarted, thereby enabling preventing ofdeterioration of the secondary battery characteristics.

The 20th invention is a charging method according to the 19th inventiondesigned to restart charging after a specified time passes from the timewhen the specified electrical condition is detected. According to thischarging method, it is possible to more effectively secure the timebefore it returns to the full-charge condition and to more improve theeffect to prevent deterioration of the secondary batterycharacteristics.

The 21st invention is a charging method according to the 19th inventiondesigned to detect that the charging current exceeds a specified valuewhen the said charging voltage or voltage lower than this chargingvoltage is applied to the said secondary battery for the detection ofthe said specified electrical condition. According to this chargingmethod, it is possible to accurately detect the secondary batterycondition from the charging current.

The 22nd invention is a charging method according to the 19th inventiondesigned to detect that the battery voltage of the said secondarybattery attains the specified voltage for the detection of the saidspecified electrical condition. According to this charging method, it ispossible to accurately detect the secondary battery condition from thebattery voltage.

The 23rd invention is a charging method according to the 22nd inventiondesigned to charge at least the energy required for detecting thebattery voltage in the said secondary battery when the said secondarybattery voltage does not attain the specified voltage and charging isnot restarted. According to this charging method, it is possible toeffectively prevent the decrease of remaining voltage caused byrepeating detection of the battery condition every specified time.

The 24th invention is a charging method according to the 22nd inventiondesigned to detect that a specified voltage lowers from the voltage setby the said charging voltage designated as a standard for detection ofthe said specified voltage. According to this charging method, it ispossible to accurately detect lowering of the battery voltage set by thecharging voltage designated as a standard, and to accurately control thesecondary battery condition.

The 25th invention is a charging method according to the 22nd inventiondesigned to detect that the battery voltage attains the specifiedvoltage value from the voltage set with the grounding potential of thesaid secondary battery designated as standard for detection of the saidspecified voltage. According to this charging method, it is possible toaccurately control the secondary battery condition by comparativelysimple voltage detection.

The 26th invention is a charging method for charging the secondarybattery which is designed to detect the electrical condition of the saidsecondary battery, to selectively supply the first and the secondvoltages to the said secondary battery in accordance with the detectedelectrical condition, and to carry out ON/OFF control of application ofthe selected voltage to the said secondary battery in accord with thesaid detected electrical condition. According to this charging method,it is possible to select the first and the second voltages for thevoltage applied to the secondary battery, and at the same time, to beable to carry out ON/OFF control for the application of the selectedvoltage, and to prevent discharge from the battery to the chargingcircuit side when charging voltage lower than the battery voltage isestablished, thereby preventing wasteful discharge of the secondarybattery when voltage applied to the secondary battery is allowed to bevaried.

The 27th invention is a charging method according to the 26th inventiondesigned to charge the secondary battery with application of thisvoltage to the said secondary battery turned off with the said secondvoltage selected when the said secondary battery is judged to be chargedto a specified value by the detection of the said electrical conditionafter the said first voltage is selected and applied to charge the saidsecondary battery when the charging voltage of the said secondarybattery is lower than the specified value by the detection of the saidelectrical condition, and it is also designed to charge the secondarybattery with the application of the said second voltage to the saidsecondary battery turned on when the secondary battery voltage is judgedto be lower than the said second voltage. According to this chargingmethod, it is possible to effectively prevent wasteful discharge fromthe secondary battery and at the same time to be able to charge thesecond voltage to the secondary battery free of detrimental effects whencharging is restarted.

The 28th invention is a charging method according to the 27th inventiondesigned to judge that the said secondary battery voltage is lower thanthe said second voltage when it is judged that the voltage is lower thanthe said second voltage again in a specified time after it is judged atleast once that the voltage is lower than the said second voltage.According to this charging method, it is possible to charge thesecondary battery with the second voltage when the secondary batteryvoltage is positively lower than the second voltage and to restartcharging under the favorable condition free of deteriorating thesecondary battery.

The 29th invention is a charging method according to the 27th inventiondesigned to apply the said second voltage to the secondary battery forcharging when it is judged that the secondary battery voltage is thethird voltage lower than the second voltage. According to this chargingmethod, it is possible to restart charging under the favorable conditionfree of deteriorating the secondary battery only by judgment of thebattery voltage without counting passage of time.

The 30th invention is a charging method according to the 27th inventiondesigned to detect the potential difference between one end and theother end of a switching means for carrying out the said ON/OFF controland judge that the said secondary battery voltage is lower than thesecond voltage. According to this charging method, it is possible toaccurately judge the battery voltage at the restart of charging.

The 31st invention is a charging method according to the 27th inventiondesigned to judge that the said secondary battery voltage is lower thanthe said second voltage when the current of the said secondary batteryis judged to be lower than the specified current value when voltageapplication to the said secondary battery is turned off. According tothis charging method, charging process at the second voltage is carriedout only when the current flowing in the load circuit is lower than thespecified value (for example, in the case of the vicinity of zero), andit is possible to prevent charging at a low voltage when the loadcurrent exceeds the specified value.

The 32nd invention is a charging method according to the 27th inventiondesigned to detect the potential difference between one end and theother end of a switching means for carrying out the ON/OFF control whenthe said secondary battery current is lower than the specified currentwhen the application of voltage to the said secondary battery is turnedoff and to judge that the said secondary battery voltage is lower thanthe said second voltage. According to this charging method, it ispossible to judge the restart of charging by accurate voltage judgmentbased on the potential difference between one end and the other end ofthe switching means only when the current flowing in the load current islower than the specified value.

The 33rd invention is a charging method according to the 26th inventiondesigned to select the second voltage and charge with the application ofvoltage to the said secondary battery turned on when the current flowingin the secondary battery again at least after a specified time is judgedto be lower than the said specified value after the current flowing inthe secondary battery is judged to be lower than the specified valueunder the condition in which this second voltage is selected with theapplication of voltage to the secondary battery turned off under thecondition in which the second voltage is selected when the voltage ischarged with the application of the voltage to the secondary batteryturned on with the first voltage selected when the charged voltage ofthe secondary battery is judged to be lower than the specified value.According to this charging method, it is possible to effectively preventwasteful discharge from the secondary battery as well as to judge therestart of charging based on judgment of the current.

The 34th invention is a charging method according to the 33rd inventiondesigned to detect the current flowing in the current path connected tothe said secondary battery different from the current path fed to thesaid secondary battery via a switching means for carrying out the saidON/OFF control from a means for supplying the said first and the secondvoltages for detection of the current flowing to the said secondarybattery. According to this charging method, it is possible to detect thestable current value not subject to fluctuation of voltage applied.

The 35th invention is a charging method according to the 26th inventiondesigned to provide the first and the second switching means in parallelas switching means to carry out the said ON/OFF control and to supplyconstant current to the second switching means, and when the chargedvolume of the secondary battery is lower than the specified volume, itis designed to charge the secondary battery with the first switchingmeans turned on and the second switching means turned off under thecondition in which the first voltage is selected when the chargingvolume of the secondary battery is judged to be lower than the specifiedvolume, and when the charged volume of the secondary battery is judgedto be charged to the specified volume, it is designed to turn off thefirst and the second switching means with the second voltage selected,and when the secondary battery voltage is judged to be lower than thesecond voltage with the second voltage selected, it is designed to turnon the second switching means and to supply the said constant current tothe secondary battery for charging. According to this charging method,it is possible to achieve favorable charging by constant current.

The 36th invention is a charging equipment for charging the secondarybattery which is charged by constant charging voltage, comprising afirst voltage feeding means for feeding the first voltage to thesecondary battery, a second voltage feeding means for feeding the secondvoltage lower than the first voltage to the secondary battery, a currentdetection means for detecting charging current to the secondary battery,and a control means for changing over the supply by the first voltagefeeding means to and from the supply by the second voltage feeding meansbased on the detection results by the said current detection means,wherein when the current detecting means detects the first chargingcurrent corresponding to nearly full-charge by the current detectionmeans, the supply to the secondary battery is changed over from thefirst voltage feeding means to the second voltage feeding means, and atthe same time, when the current detection means detects currentexceeding the second charging current with the second voltage fed to thesecondary battery from the second voltage feeding means by thischange-over, the supply is changed over to that by the first voltagefeeding means. According to this charging equipment, the battery ischarged to the full-charge condition by the first voltage only when thebattery charging remainder lowers to a specified value. Consequently,once it is charged to the full-charge condition, charging to thefull-charge is repeated every time the battery lowers to the specifiedbattery charging remainder and the secondary battery is able to beconstantly maintained to nearly full-charge condition, and at the sametime, because the second voltage lower than the first voltage is appliedto the battery except when charging to this full-charge is carried out,the secondary battery is not brought to continuous full-chargecondition, and deterioration of secondary battery performance caused bycontinued full-charge condition can be prevented.

The 37th invention is the charging equipment according to the 36thinvention wherein the first charging current is the same as the secondcharging current. According to this charging equipment, the chargingcondition can be favorably controlled.

The 38th invention is the charging equipment according to the 36thinvention, comprising the third voltage feeding means for feeding thethird voltage of the potential across the first and the second voltagesto the secondary battery, and a temperature detection means fordetecting temperature inside or in the vicinity of the secondarybattery, wherein only when the detected temperature of the secondarybattery exceeds a predetermine temperature, the second voltage feedingmeans is changed over to the third voltage feeding means in place ofchanging over from the second voltage feeding means to the first voltagefeeding means. According to this charging equipment, chargingcorresponding to temperature is favorably controlled.

The 39th invention is designed to continuously change the output voltageof the third voltage feeding means in accord with temperature detectedby the temperature detection means in the charging equipment accordingto the 38th invention. According to this charging equipment, it ispossible to finely control the charging voltage in accord with the thentemperature at that time, and charging control corresponding totemperature can be favorably carried out.

The 40th invention is the charging equipment for charging the secondarybattery in which charging is carried out by the constant voltagecharging voltage, comprising a first voltage feeding means for feedingthe first voltage to the secondary battery, a second voltage feedingmeans for feeding the second voltage lower than the first voltage to thesecondary battery, a current detection means for detecting the chargingcurrent to the secondary battery, a voltage detecting means fordetecting one voltage of the secondary battery, and a control means forchanging over the supply by the first voltage feeding means to and fromthe supply by the second voltage feeding means based on the detectedresult by the voltage detecting means, wherein when the specifiedvoltage corresponding to the condition in which the secondary battery isnearly fully charged is detected by the voltage detection means, thesupply to the secondary battery is changed over from the first voltagefeeding means to the second voltage feeding means, and when the currentdetection means detects the current exceeding the predetermined chargingcurrent with the second voltage supplied from the second voltage feedingmeans to the secondary battery by this change-over, the supply ischanged over by the first voltage feeding means. According to thischarging equipment, the battery is charged to the full-charge conditionby the first voltage only when the battery charging remainder lowers tothe specified value. Consequently, after the battery is charged to thefull-charge condition once, charging to the full-charge is repeatedevery time the battery charging remainder lowers to a specified volume,and the secondary battery can constantly be maintained to a nearlycharged condition, and at the same time, because the second voltagelower than the first voltage is applied to the battery except whencharging to the full-charge is carried out, the secondary battery is notbrought continuously to the full-charged condition, thereby preventingdeterioration of the secondary battery performance caused by thecontinuation of the full-charged condition.

The 41st invention is the charging equipment according to the 40thinvention, comprising the third voltage feeding means for feeding thethird voltage of the potential across the first and the second voltageto the secondary battery and a temperature detection means for detectingthe temperature inside or in the vicinity of the secondary battery,wherein when the detection temperature of the said temperature detectingmeans exceeds a specified temperature, the voltage feeding means ischanged over to the third voltage feeding means in place of changingover from the second voltage feeding means to the first voltage feedingmeans. According to this charging equipment, charging is able to befavorably controlled in accord with the temperature.

The 42nd invention is the charging equipment according to the 41stinvention, wherein the output voltage of the said third voltage feedingmeans is designed to be continuously changed in accord with thetemperature detected by the said temperature detecting means. Accordingto this charging equipment, it is possible to finely control thecharging voltage in accord with the then temperature and to favorablycontrol charging in accord with the temperature.

The 43rd invention is the charging equipment for charging the secondarybattery requiring constant current charging at the start of charging,comprising a power supply circuit for feeding the specified chargingpower supply to the secondary battery, a switching means connectedacross the said power supply circuit and the said secondary battery forcontrolling the start and stop of charging, a detecting means fordetecting the potential across one end and the other end of the saidswitching means or the potential across one end and the other end of thesaid secondary battery with the low-voltage charging power supply fedfrom the said power supply circuit, and a charging control means forstarting charging to the secondary battery with the said switching meansturned on based on the potential detected by the said detection means aswell as the output voltage of the said power supply circuit set to aspecified potential. According to this charging equipment, it ispossible to detect the secondary battery condition based on the controlof the switching means and the detection of the potential across one endan the other end of the switching means or the potential across one endand the other end of the secondary battery, and to accurately detect thecondition of the secondary battery as in the case of the conventionalpre-charging. Consequently, it is possible to precisely detect thesecondary battery condition without providing a charging circuit specialfor pre-charging and simplify the circuit configuration of the chargingequipment.

The 44th invention is the charging equipment according to the 43rdinvention, wherein a field-effect transistor is used for the saidswitching means, and the potential is designed to be detected by thesaid detection means by increasing the impedance value across one endand the other end of the field-effect transistor. According to thischarging equipment, the condition of the secondary battery can be easilydetected only by controlling the impedance of the field-effecttransistor, and at the same time, even when the secondary batteryvoltage is low or shorted, it is possible to minimize the loss of thefield-effect transistor, and to minimize the size of the transistoritself and a radiation plate, contributing to downsizing of the chargingequipment.

The 45th invention is the charging equipment according to the 43rdinvention, wherein the output potential of the said power supply circuitwhen detected by the above detection means is set to the value in thevicinity of the lowest voltage at which the said charging control meansoperates. According to this charging equipment, it is possible to detectthe secondary battery condition with the charging power supply of thelowest voltage fed to the secondary battery, to detect the electricalcondition of the secondary battery with the load to the secondarybattery or circuit brought to the minimum, and to detect the electricalcondition of the secondary battery under the favorable condition.

The 46th invention is the charging equipment according to the 43rdinvention, wherein the output voltage of the said power supply isdesigned to increase with an increase of the potential across one endand the other end of the secondary voltage after the start of charging.According to this charging equipment, the power applied to the switchingmeans is able to be held nearly uniformly, and the condition of theswitching means is able to be held favorably.

The 47th invention is the charging equipment according to the 43rdinvention, wherein the output voltage of the said power supply circuitis designed to be varied in a plurality of stages with an increase ofthe potential across one end and the other end of the said secondarybattery after the start of charging. According to this chargingequipment, it is possible to keep the power supply applied to theswitching means nearly uniformly and to keep the condition of theswitching means in the favorable condition. In this event, because thevoltage is able to be varied in the plurality of stages, only simplifiedcontrol is required for control of the voltage circuit.

The 48th invention is the charging equipment according to the 43rdinvention, wherein a charged load storage means is connected across thesaid power supply circuit and the said charging control means, and tolower the output potential of the said power supply circuit whendetected by the said detection means to the minimum voltage at which thecharging control means lowers. According to this charging equipment, aslong as electric charge is accumulated in the electric charge storagemeans, voltage of the charging power supply to be fed to the secondarybattery in detecting by the detection means can be brought to thevoltage lower than the voltage for controlling the switching means, andthe condition of the secondary battery can be detected more favorablywith the still lower voltage applied.

The 49th invention is the charging equipment for charging the secondarybattery to be charged by the constant voltage charging voltage,comprising a constant-voltage means for feeding the said chargingvoltage to the said secondary battery, a battery condition detectingmeans for detecting the said secondary battery condition, a chargingcontrol means for controlling charging by the constant-voltage means,and a timer means which operates when the said battery conditiondetecting means detects the specified condition of the said secondarybattery, wherein a specified time passes from the start of operation ofthe timer means, the charging control means is designed to startcharging by the said constant voltage means. According to this chargingequipment, it is possible to designate the time from the time when thebattery once attains the full-charged condition (or nearly full-chargedcondition) to the time when charging is restarted as the time requiredfor the battery to attain a specified electrical condition with aspecified time added, thereby securing some time before the batteryreturns to the full-charged condition even if an error occurs in thedetection of the battery condition, and it is possible to preventdeterioration of secondary battery characteristics caused by thecontinued full-charged condition.

The 50th invention is the charging equipment according to the 49thinvention, wherein the said battery condition detection means isdesigned to detect the condition in which the secondary battery voltageattains a specified voltage. According to this charging equipment, it ispossible to accurately detect the lowering of battery voltage with thecharging voltage set as a standard, enabling accurate control of thesecondary battery condition.

The 51st invention is the charging equipment according to the 49thinvention, wherein the said battery condition detection means isdesigned to detect the condition in which the charging current attainsthe specified value when the specified voltage is applied to the abovesecondary battery. According to this charging equipment, it is possibleto properly control the charging condition of the secondary batterybased on the detection of the current value.

The 52nd invention is the charging equipment according to the 49thinvention, wherein the constant voltage for pre-charging lower than thesaid charging voltage is designed to be fed as the said constant voltagemeans and this constant voltage for pre-charging is designed to be usedfor the specified voltage applied to the said secondary battery.According to this charging equipment, it is possible to favorably setthe voltage applied at the time of precharging.

The 53rd invention is the charging equipment for charging the secondarybattery in which charging takes place by constant voltage chargingvoltage, comprising a constant voltage means for supplying the saidcharging voltage to the secondary battery, a battery condition detectionmeans for detecting the said secondary battery condition, a chargingcontrol means for controlling charging by the said constant voltagemeans, and a timer means for operating when the said battery conditiondetection means detects the nearly charged condition of the saidsecondary battery, wherein the said charging control means allows thesaid battery condition detection means to detect the condition of thesaid secondary battery every time nearly a specified time passes fromthe time when the said timer means begins to operate, and when thisdetected condition falls in the specified condition, charging by thesaid constant voltage means is designed to be restarted. According tothis charging equipment, it is possible to keep at least a predeterminedtime open for the specified period from the time when charging isstopped once full-charge condition is attained to the time when chargingis restarted, thereby enabling preventing of deterioration of thesecondary battery characteristics.

The 54th invention is the charging equipment according to the 53rdinvention, wherein charging by the constant voltage means is restartedafter a specified time passes from the time when the specified conditionis detected. According to this charging equipment, it is possible tomore effectively secure the time before it returns to the full-chargecondition and to more improve the effect to prevent deterioration of thesecondary battery characteristics.

The 55th invention is the charging equipment according to the 53rdinvention, wherein the said battery condition detection means isdesigned to detect as the specified condition detection that thecharging current exceeds a specified value when the said chargingvoltage or voltage lower than this charging voltage is applied to thesaid secondary battery. According to this charging equipment, it ispossible to accurately detect the secondary battery condition from thecharging current.

The 56th invention is the charging equipment according to the 53rdinvention, wherein the said battery condition detection means isdesigned to detect as the specified condition detection that the batteryvoltage of the said secondary battery attains the specified voltage.According to this charging equipment, it is possible to accuratelydetect the secondary battery condition from the battery voltage.

The 57th invention is the charging equipment according to the 56thinvention, wherein at least the energy required for detecting thebattery voltage in the said secondary battery is designed to be chargedin the secondary battery by the control of the said charging controlmeans when the said secondary battery voltage does not attain thespecified voltage and charging is not restarted. According to thischarging equipment, it is possible to effectively prevent the decreaseof remaining voltage caused by repeating detection of the batterycondition every specified time.

The 58th invention is the charging equipment for charging the secondarybattery, comprising a first voltage supply means for supplying the firstvoltage to the secondary battery, a second voltage supply means forsupplying the second voltage lower than the said first voltage to thesecondary battery, a selection means for changing over the chargingvoltage applied to the said secondary battery between the said first andsecond voltage supply means, a switching means for ON-OFF controllingthe application of the output voltage of the first or second voltagesupply means selected by the selection means to the secondary battery, adetecting means for detecting the electrical condition of the saidsecondary battery, and a control means for controlling the selectionwith the said selection means and ON/OFF control by the said change-overmeans in accord with the condition detected by the detection means.According to this charging equipment, it is possible to select the firstand the second voltages for the voltage applied to the secondarybattery, and at the same time, to be able to carry out ON-OFF control ofthe application of this selected voltage, to prevent discharge from thebattery to the charging circuit side when charging voltage lower thanthe battery voltage is established, thereby preventing wastefuldischarge of the secondary battery when voltage applied to the secondarybattery is allowed to be varied.

The 59th invention is the charging equipment according to the 58thinvention, wherein when the said control means judges that the chargedvolume of the secondary battery is lower than the specified volume, thesaid switching means is turned on and at the same time the first voltagesupply means is selected by the selection means to apply the firstvoltage to the secondary battery for charging, and when the said controlmeans judges that the secondary battery is charged to the specifiedvolume, the said switching means is turned off, and at the same time thesecond voltage feeding means is selected by the said selection means,and when the said control means judges that the secondary batteryvoltage is lower than the second voltage under the state that the secondvoltage feeding means is selected, the switching means is turned on bycontrol of the said control means to apply the second voltage to thesecondary battery for charging. According to this charging equipment, itis possible to effectively prevent wasteful discharge from the secondarybattery and at the same time to be able to charge the second voltage tothe secondary battery free of detrimental effects when charging isrestarted.

The 60th invention is the charging equipment according to the 59thinvention, wherein for the said control means to judge that thesecondary battery voltage is lower than the second voltage is when it isjudged that the voltage is lower than the second voltage again in aspecified time after it is judged at least once that the voltage islower than the second voltage. According to this charging equipment, itis possible to charge the secondary battery with the second voltage whenthe secondary battery voltage is positively lower than the secondvoltage and to restart charging under the favorable condition free ofdeteriorating the secondary battery.

The 61st invention is the charging equipment according to the 59thinvention, wherein it is when the secondary battery voltage is the thirdvoltage lower than the second voltage that the second voltage feedingmeans applies the said second voltage to the secondary battery forcharging. According to this charging equipment, it is possible torestart charging under the favorable condition free of deteriorating thesecondary battery only by judgment of the battery voltage withoutcounting passage of time.

The 62nd invention is the charging equipment according to the 59thinvention, wherein the potential difference between one end and theother end of the switching means is detected for judging that the saidsecondary battery voltage is lower than the second voltage. According tothis charging equipment, it is possible to accurately judge the batteryvoltage at the restart of charging.

The 63rd invention is the charging equipment according to the 59thinvention, wherein it is judged whether or not the said secondarybattery voltage is lower than the said second voltage when the currentof the said secondary battery is judged to be lower than the specifiedcurrent value when the said switching means is turned off. According tothis charging equipment, charging processing at the second voltage iscarried out only when the current flowing in the load circuit is lowerthan the specified value (for example, in the case of the vicinity ofzero), and it is possible to prevent charging at a low voltage when theload current exceeds the specified value.

The 64th invention is the charging equipment according to the 59thinvention, wherein the potential difference between one end and theother end of the switching means is detected when the said secondarybattery current is judged lower than the specified current when the saidswitching means is turned off and it is judged that the said secondarybattery voltage is lower than the said second voltage. According to thischarging equipment, it is possible to judge the restart of charging byaccurate voltage judgment based on the potential difference between oneend and the other end of the switching means only when the currentflowing in the load current is lower than the specified value.

The 65th invention is the charging equipment according to the 58thinvention, wherein when the said control means judges that the chargedvolume of the secondary battery is lower than the specified volume, theswitching means is turned on and at the same time, the first voltagefeeding means is selected with the said selecting means to apply andcharge the first voltage to the secondary battery, and when the controlmeans judges that the charged volume of the secondary battery is chargedto the specified volume, the switching means is turned off, and at thesame time the second voltage feeding means is selected by the saidselecting means, and the second voltage is applied to the secondarybattery to change the same with the switching means turned on by thecontrol of the control means when the current flowing in the secondarybattery is judged again to be lower than the specified value at least inthe specified time after the control means judges that the currentflowing in the secondary battery is lower than the specified value withthis second voltage feeding means selected. According to this chargingequipment, it is possible to effectively prevent wasteful discharge fromthe secondary battery as well as to judge the restart of charging basedon judgment of the current.

The 66th invention is the charging equipment according to the 65thinvention, wherein the current flowing in the current path connected tothe said secondary battery different from the current path fed to thesaid secondary battery via the switching means is detected for thecurrent flowing to the said secondary battery. According to thischarging equipment, it is possible to detect the stable current valuenot subject to fluctuation of voltage applied.

The 67th invention is the charging equipment according to the 58thinvention, wherein the first and the second switching means are providedin parallel as the said switching means and a constant current outputmeans is connected to the second switching means, and when the chargedvolume of the secondary battery is judged to be lower than the specifiedvolume, the first switching means is turned on and the second switchingmeans is turned off, and at the same time the first voltage feedingmeans is selected by the selecting means to apply and charge the firstvoltage to the secondary battery, and when the control means judges thatthe charged volume of the secondary battery is charged to the specifiedvolume, the first and the second switching means are turned off and thesecond voltage feeding means is selected with the selecting means, andwhen the control means judges that the second battery voltage is lowerthan the second voltage with this second voltage feeding means selected,the control means controls to turn on the second switching means and toturn off the first switching means, and the output of the constantcurrent output means is supplied to charge the secondary battery.According to this charging equipment, it is possible to achievefavorable charging by constant current.

The 68th invention is an integrated circuit for controlling charging ofthe secondary battery in which control is carried out for selectivelysupplying the first voltage and the second voltage lower than this firstvoltage to the said secondary battery, and when the secondary battery isjudged to be nearly fully charged based on the judgment of the detectedcharging current while control is being carried out for applying andcharging the first voltage to the secondary battery, control is carriedout for changing over to the application of the second voltage to thesecondary battery, and when the secondary battery is judged to have aspecified battery remaining voltage based on the judgment of thedetected charging current while control of applying this second voltageis being underway, control is carried out for changing over to theapplication of the first voltage to the secondary battery. According tothis integrated circuit, control for charging to the full-chargecondition by the first voltage is carried out only when the remainingbattery volume lowers to the specified volume. Consequently, after thebattery is charged to the full-charge condition once, charging to thefull-charge is repeatedly carried out every time the battery lowers tothe specified battery charging remainder, thereby maintaining thesecondary battery condition constantly to the nearly full-chargecondition, and at the same time, because except when charging to thisfull-charging is carried out, the second voltage lower than the firstvoltage is applied to the battery, the secondary battery does not reachthe full-charge condition continuously, enabling favorable chargingcontrol in which deterioration of the secondary battery performancecaused by continued full-charge condition can be prevented.

The 69th invention is an integrated circuit according to the 68thinvention, wherein when the temperature is higher than a specifiedtemperature based on the judgment of the detected temperature inside orin the vicinity of the secondary battery, control is carried out forapplying the third voltage across the first voltage and the secondvoltage to the secondary battery. According to this integrated circuit,it is possible to favorably carry out charging control while suppressingthe deterioration of performance of the secondary battery due totemperature rise of the battery.

The 70th invention is an integrated circuit according to the 69thinvention, wherein the third voltage is controlled to be continuouslyvaried based on the judged temperature. According to this integratedcircuit, the charging voltage can be finely controlled in accord withthe temperature at the time and charging can be more favorably carriedout in accord with temperature.

The 71st invention is an integrated circuit for controlling charging ofthe secondary battery in which control is carried out for selectivelysupplying the first voltage or the second voltage lower than this firstvoltage to the said secondary battery, and when the secondary battery isjudged to be nearly fully charged based on the judgment of the detectedcharging voltage while control is being carried out for applying andcharging the first voltage to the secondary battery, control is carriedout for changing over to the application of the second voltage to thesecondary battery, and when the secondary battery is judged to have aspecified battery remaining voltage based on the judgment of thedetected charging voltage while control of applying this second voltageis being underway, control is carried out for changing over to theapplication of the first voltage to the secondary battery. According tothis integrated circuit, control for charging to the full-chargecondition by the first voltage is carried out only when the remainingbattery volume lowers to the specified volume. Consequently, after thebattery is charged to the full-charge condition once, charging to thefull-charge is repeatedly carried out every time the battery lowers tothe specified battery charging remainder, thereby maintaining thesecondary battery condition constantly to the nearly full-chargecondition, and at the same time, because except when charging to thisfull-charging is carried out, the second voltage lower than the firstvoltage is applied to the battery, the secondary battery does not reachthe full-charge condition continuously, enabling favorable chargingcontrol in which deterioration of the secondary battery performancecaused by continued full-charge condition can be prevented.

The 72nd invention is an integrated circuit according to the 71stinvention, wherein when the temperature is higher than the specifiedtemperature based on the judgment of the detected temperature inside orin the vicinity of the secondary battery, control is carried out forapplying the third voltage across the first voltage and the secondvoltage to the secondary battery. According to this integrated circuit,it is possible to favorably carry out charging control while suppressingthe deterioration of performance of the secondary battery due totemperature rise of the battery.

The 73rd invention is an integrated circuit according to the 69thinvention, wherein the third voltage is controlled to be continuouslyvaried based on the judged temperature. According to this integratedcircuit, the charging voltage can be finely controlled in accord withthe temperature at the time and control of charging can be morefavorably carried out in accord with temperature.

The 74th invention is an integrated circuit for controlling charging ofthe secondary battery, wherein the detected value of the potentialacross one end and the other end of the switching means for controllingstart and stop of the supply of the charging power supply to thesecondary battery or the potential across one end and the other end ofthe secondary battery is judged while control for supplying thelow-voltage charging power supply to the secondary battery is beingcarried out, and when this judged potential is a specified potential,control for turning on the switching means is carried out and at thesame time control for setting the charging power supply supplied to thesecondary battery to the specified potential is carried out so thatcontrol for starting the charging to the secondary battery takes place.According to this integrated circuit, it is possible to control theswitching means and to detect the secondary battery condition based onthe detection of the potential across one end and the other end of thisswitching means or the potential across one end and the other end of thesecondary battery, thereby enabling accurate detection of the secondarybattery condition as in the case of conventional pre-charging.Consequently, it is possible to precisely detect the secondary batterywithout providing a charging circuit specialized for pre-charging, andit is possible to simplify the circuit configuration of the chargingequipment.

The 75th invention is an integrated circuit according to the 74thinvention, wherein the detected value of the potential across one endand the other end of the secondary battery after the said chargingbegins is judged, and control is carried out to raise the potential ofthe charging power supply in accordance with the increase of the judgedpotential. According to this integrated circuit, it is possible to holdthe power supply applied to the switching means nearly uniformly,thereby enabling the control for maintaining the switching means to afavorable condition.

The 76th invention is an integrated circuit according to the 74invention, wherein the detected value of the potential across one endand the other end of the secondary battery after the charging begins isjudged, and control for raising the potential of the charging powersupply by varying it in a plurality of stages in accord with an increaseof the judged potential. According to this integrated circuit, it ispossible to nearly uniformly keep the electric power applied to theswitching means, and it is also possible to keep the switching means tothe favorable condition. In this case, since voltage is allowed to bevaried in a plurality of stages, a simple control is only required forcontrol of the voltage circuit.

The 77th invention is an integrated circuit for controlling the chargingof the secondary battery, wherein if it is judged that the batteryreaches a specified electrical condition based on the specifiedelectrical detection data related to the secondary battery aftercarrying out the control for stopping the charging operation whencharging operation by constant voltage is carried out and it is judgedthat the secondary battery reached the nearly full-charged condition,control is carried out to restart the charging operation of thesecondary battery after a specified time passes from this judgment ofthis specified electrical condition. According to this integratedcircuit, it is possible to designate the time to restart charging onceit comes in the full-charge state (or nearly full-charge state) to thetime in which a specified time is added to the time for a battery toreach a specified electrical condition, and even if any error exists inthe detected battery condition, it is possible to secure a certain timefor returning to the full-charge condition, and it is thereby possibleto carry out favorable control to prevent deterioration ofcharacteristics of the secondary battery caused by continuation of thefull-charge conditions.

The 78th invention is an integrated circuit according to the 77thinvention, wherein the said specified electrical condition is judged byjudging that the battery voltage of the said secondary battery reachesthe specified voltage. According to this integrated circuit, it ispossible to exactly judge the condition of the secondary battery by thejudgment of the battery voltage.

The 79th invention is an integrated circuit according to the 77thinvention, wherein the said specified electrical condition is judged byjudging that the charging current reaches a specified current value whena specified voltage is applied to the secondary battery. According tothis integrated circuit, it is possible to exactly judge the secondarybattery condition by judgment of the charging current.

The 80th invention is an integrated circuit according to the 79thinvention, wherein control is made to apply the said specified voltageto the secondary battery, which is lower than the charging voltage ofthe said constant voltage. According to this integrated circuit, it ispossible to detect the secondary battery condition by the voltage lowerthan the charging voltage, and to properly detect the battery conditionwith a load applied to the secondary battery reduced.

The 81st invention is an integrated circuit for controlling the chargingof the secondary battery in which charging is carried out by constantvoltage charging to judge that the secondary battery reaches the nearlyfull-charged condition, and after control for stopping the chargingoperation is carried out, the specified electrical detection datarelated to the secondary battery is judged every time a specified timepasses from the stopping of this charging operation, and when it isjudged that the battery enters a specified electrical condition by thisjudgment, control is carried out for restarting the charging operation.According to this integrated circuit, it is possible to keep the timeopen at least for the specified period from the time when charging isstopped once full-charge condition is attained to the time when chargingis restarted, thereby enabling control while preventing thedeterioration of the secondary battery characteristics.

The 82nd invention is an integrated circuit according to the 81stinvention, wherein control is carried out to restart charging after aspecified time passes from the time when the specified electricalcondition is judged. According to this integrated circuit, it ispossible to more effectively secure the time before it returns to thefull-charge condition and to more improve the effect to preventdeterioration of the secondary battery characteristics.

The 83rd invention is an integrated circuit according to the 81stinvention, wherein the specified electrical condition is judged byjudging that the detected charging current exceeds a specified valuewhile control for applying a constant voltage or specified voltage lowerthan this constant voltage is being applied to the said secondarybattery. According to this integrated circuit, it is possible toaccurately detect the secondary battery condition from judgment of thecharging current.

The 84th invention is an integrated circuit according to the 81stinvention, wherein the specified electrical condition is judged byjudging that the detected secondary battery voltage reaches a specifiedvoltage. According to this integrated circuit, it is possible toaccurately detect the secondary battery condition from judgment of thecharging current.

The 85th invention is an integrated circuit according to the 84thinvention, wherein control is carried out so that at least the energyrequired for detecting the battery voltage in the said secondary batteryis designed to be charged to the secondary battery when it is judgedthat the detected value of the secondary battery voltage does not attainthe specified voltage and charging is not restarted. According to thisintegrated circuit, it is possible to carry out control for effectivelypreventing the decrease of remaining voltage caused by repeatingdetection of the battery condition every specified time.

The 86th invention is an integrated circuit for controlling the chargingof the secondary battery, wherein control is carried out for selectivelysupplying the first voltage and the second voltage lower than the saidfirst voltage to the secondary battery, and detected value of theelectrical condition of the secondary battery is judged, and in accordwith the judged detected value, the first voltage and the second voltageare selected for the voltage to be applied to the secondary battery, andON-OFF control is carried out for applying the selected voltage to thesecondary battery. According to this integrated circuit, it is possibleto select the first and the second voltages for the voltage applied tothe secondary battery, and at the same time, to be able to carry outON-OFF control of the application of this selected voltage, to preventdischarge from the battery to the charging circuit side when chargingvoltage lower than the battery voltage is established, and to enable thecontrol for preventing wasteful discharge of the secondary battery whenvoltage applied to the secondary battery is allowed to be varied.

The 87th invention is an integrated circuit according to the 86thinvention, wherein when based on the judgment of the detection value ofthe electrical condition of the said secondary battery, it is judgedthat the secondary battery is charged to the specified volume, thesecond voltage is selected and at the same time control for turning offthe application of this voltage to the secondary battery, and if it isjudged that under this condition, the secondary battery voltage reachesbelow the second voltage, control for turning on the application of thesecond voltage to the secondary battery is carried out. According tothis integrated circuit, it is possible to effectively prevent wastefuldischarge from the secondary battery and at the same time to be able tocontrol of the charging of the second voltage to the secondary batteryfree of detrimental effects when charging is restarted.

The 88th invention is an integrated circuit according to the 87thinvention, wherein to judge that the secondary battery voltage is lowerthan the second voltage is when it is judged that the voltage is lowerthan the second voltage again in a specified time after it is judged atleast once that the voltage is lower than the second voltage. Accordingto this integrated circuit, it is possible to charge the secondarybattery with the second voltage when the secondary battery voltage ispositively lower than the second voltage and to restart charging underthe favorable condition free of deteriorating the secondary battery.

The 89th invention is an integrated circuit according to the 87thinvention, wherein it is when it is judged that the secondary batteryvoltage is the third voltage lower than the second voltage that the saidsecond voltage is applied and charged to the secondary battery.According to this integrated circuit, it is possible to restart chargingunder the favorable condition free of deteriorating the secondarybattery only by judgment of the battery voltage without counting passageof time.

The 90th invention is an integrated circuit according to the 87thinvention, wherein it is judged that the said secondary battery voltageis lower than the said second voltage when the current of the saidsecondary battery is judged to be lower than the specified current valuewhen voltage application to the said secondary battery is turned off.According to this integrated circuit, charging processing at the secondvoltage is carried out only when the current flowing in the load circuitis lower than the specified value (for example, in the case of thevicinity of zero), and it is possible to prevent charging at a lowvoltage when the load current exceeds the specified value.

The 91st invention is an integrated circuit according to the 87thinvention, wherein when the secondary battery current is judged to belower than the specified value when application of the voltage to thesecondary battery is turned off, the potential difference between oneend and the other end of the switching means for carrying out the ON/OFFcontrol is detected and the secondary battery voltage is judged to belower than the second voltage. According to this integrated circuit, itis possible to judge the restart of charging by accurate voltagejudgment based on the potential difference between one end and the otherend of the switching means only when the current flowing in the loadcurrent is lower than the specified value.

The 92nd invention is an integrated circuit according to the 86thinvention, wherein when it is judged that the charged volume of thesecondary battery is lower than the specified volume, control is carriedout for turning on the application of the voltage to the secondarybattery to charge the same with the first voltage selected, and when itis judged that the secondary battery is charged to the specified volume,control is carried out for turning off the application of the voltage tothe secondary battery with the second voltage selected, and when it isjudged that the current flowing in the secondary battery again at leastafter a specified time after it is judged that the current flowing inthe secondary battery is lower than the specified value with this secondvoltage selected, control is carried out for selecting the secondvoltage and turning on the application of the voltage to the secondaryvoltage for charging. According to this integrated circuit, it ispossible to effectively prevent wasteful discharge from the secondarybattery as well as to judge the restart of charging based on judgment ofthe current.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an explanatory diagram showing one example of chargingcharacteristics of a lithium ion battery.

FIG. 2 is a structural diagram showing one example of a conventionalcharging equipment.

FIG. 3 is a characteristic diagram showing charging characteristics ofthe example of FIG. 2.

FIG. 4 is a structural diagram showing another example of theconventional charging equipment.

FIG. 5 is a characteristic diagram showing charging characteristics ofthe example of FIG. 4.

FIG. 6 is a characteristic diagram showing one example of the rechargingcondition of the conventional lithium battery.

FIG. 7 is a structural diagram showing a charging equipment according tothe first embodiment of this invention.

FIG. 8 is a flow chart showing charging processing according to thefirst embodiment.

FIG. 9 is a characteristic diagram showing the charging conditionaccording to the first embodiment.

FIG. 10 is a flow chart showing charging processing when full-chargedetection is carried out by another processing in the first embodiment.

FIG. 11 is a flow chart showing charging processing when full-chargedetection is carried out by still another processing in the firstembodiment.

FIG. 12 is a flow chart showing charging processing when full-chargedetection is carried out by still further processing in the firstembodiment.

FIG. 13 is a flow chart when control of charging processing at the timeof full-charge of the first embodiment is carried out by temperature.

FIG. 14 is a structural diagram showing a charging equipment accordingto the second embodiment of this invention.

FIG. 15 is a flow chart showing charging processing according to thesecond embodiment.

FIG. 16 is a characteristic diagram showing the charging conditionaccording to the second embodiment.

FIG. 17 is a flow chart showing the charging processing when voltage isvaried in the three stages by temperature in the second embodiment.

FIG. 18 is a structural diagram showing a charging equipment accordingto the third embodiment of this invention.

FIG. 19 is a flow chart showing charging processing according to thethird embodiment.

FIG. 20 is a structural diagram showing a charging equipment accordingto the fourth embodiment of this invention.

FIG. 21 is a flow chart showing charging processing according to thefourth embodiment.

FIG. 22 is a flow chart showing charging processing according to thefifth embodiment of this invention.

FIG. 23 is a structural diagram showing a charging equipment accordingto the sixth embodiment of this invention.

FIG. 24 is a flow chart showing charging processing according to thesixth embodiment.

FIG. 25 is a characteristic diagram showing the charging conditionaccording to the sixth embodiment.

FIG. 26 is a structural diagram showing a charging equipment accordingto the seventh embodiment of this invention.

FIG. 27 is a characteristic diagram showing the charging conditionaccording to the seventh embodiment.

FIG. 28 is a structural diagram showing a charging equipment accordingto the eighth embodiment of this invention.

FIG. 29 is a structural diagram showing a charging equipment applied tothe ninth embodiment of this invention.

FIG. 30 is a flow chart showing charging processing according to theninth embodiment.

FIG. 31 is a characteristic diagram showing the charging conditionaccording to the ninth embodiment.

FIG. 32 is a flow chart showing charging processing when full-chargedetection is carried out by another processing in the ninth embodiment.

FIG. 33 is a characteristic diagram showing the charging conditionaccording to the example of FIG. 32.

FIG. 34 is a flow chart showing charging processing according to thetenth embodiment of this invention.

FIG. 35 is a characteristic diagram showing the charging conditionaccording to the tenth embodiment.

FIG. 36 is a flow chart showing charging processing when full-chargedetection is carried out by another processing in the tenth embodiment.

FIG. 37 is a flow chart showing charging processing when full-chargedetection is carried out by still another processing in the tenthembodiment.

FIG. 38 is a characteristic diagram showing the charging conditionaccording to the 11th embodiment of this invention.

FIG. 39 is a structural diagram showing a charging equipment accordingto the 12th embodiment of this invention.

FIG. 40 is a flow chart showing charging processing by the 12thembodiment.

FIG. 41 is a flow chart showing charging condition by the modifiedexample of the 12th embodiment.

FIG. 42 is a structural diagram showing a charging equipment accordingto the 13th embodiment of this invention.

FIG. 43 is a flow chart showing charging processing by the 13thembodiment.

FIG. 44 is a structural diagram showing a charging equipment accordingto the 14th embodiment of this invention.

FIG. 45 is a flow chart showing charging processing by the 14thembodiment.

FIG. 46 is a structural diagram showing a charging equipment accordingto the 15th embodiment of this invention.

FIG. 47 is a flow chart showing charging processing by the 15thembodiment.

FIG. 48 is a structural diagram showing a charging equipment accordingto the 16th embodiment of this invention.

FIG. 49 is a flow chart showing charging processing by the 16thembodiment.

FIG. 50 is a structural diagram showing a charging equipment accordingto the 17th embodiment of this invention.

FIG. 51 is a structural diagram showing a charging equipment accordingto the 18th embodiment of this invention.

FIG. 52 is a flow chart showing charging processing by the 18thembodiment.

BEST MODE FOR CARRYING OUT THE INVENTION

Now, the first embodiment of this invention will be described withreference to FIG. 7-FIG. 13.

FIG. 7 is a block diagram showing the configuration of the chargingequipment of this embodiment, where AC power supply (about 100V-240V)from a commercial AC power supply 11 is supplied to atransformer/rectifier circuit 12 to provide a DC low-voltage powersupply. This DC low-voltage power supply is supplied to a constantcurrent circuit 13 to produce an output of constant current. And thisconstant-current output is supplied to a movable contact 14m of achange-over switch 14. First and second fixed contacts 14a and 14b ofthis change-over switch 14 are connected to constant voltage circuits 15and 16, respectively, and a specified voltage is outputted from theconstant voltage circuit 15 or 16 on the side to which the movablecontact 14m is connected. In this event, the constant voltage circuit 15is designed to output 4.2V, while the constant voltage circuit 16 isdesigned to output 4.0V.

To the positive electrode side of a secondary battery 17 loaded on thischarging equipment, the output voltage of the constant voltage circuit15 or 16 is applied. In this event, in this example, a lithium ionbattery is used for the secondary battery 17. The lithium ion batteryused here must provide characteristics in which the battery voltage is4.2V when the battery is 100% charged (fully charged).

Then, the potential difference between the positive electrode side andthe negative electrode side of this secondary battery 17 is detectedwith a voltage detection circuit 18. The data of voltage values detectedby this voltage detection circuit 18 is supplied to a control circuit 21later described.

The negative electrode side of the secondary battery 17 is connected tothe transformer/rectifier circuit 12 via a current detection resistor 19to form a charging circuit of the secondary battery 17. Based on thepotential difference between one end and the other end of the currentdetection resistor 19, the current flowing through the resistor 19 isdetected by a current detection circuit 20. The current value detectedby this current detection circuit 20 corresponds to the charging currentsupplied to the secondary battery 17. The data of current valuesdetected by the current detection circuit 20 is supplied to the controlcircuit 21. This control circuit 21 is a circuit composed by amicrocomputer with integrated circuits for controlling the chargingoperation, and based on the comparison between the data of currentvalues detected by the current detection circuit 20 and a current valueI₁ stored in advance in the control circuit 21, the connection conditionof the movable contact 14m of the change-over switch 14 is controlled.In this event, for this current value I₁, the charging current valuewhen the secondary battery 17 is 100% charged with the charging voltage4.2V is used.

By the way, there is a case in which a load circuit 28 may be connectedto the secondary battery 17.

Now, referring to the flow chart of FIG. 8, processing when thesecondary battery (lithium ion battery) is charged with this chargingequipment will be described.

First of all, the control circuit 21 detects whether there is thesecondary battery 17 or not (that is, whether it is loaded on thecharging equipment or not) (Step S101). The presence of the battery 17is judged by electrical detection, such as detection of the batteryvoltage and so on or mechanical detection, and either detection isacceptable.

Based on the detection results, whether the battery is present or not isjudged (Step S102), and if it is judged that the battery is present, themovable contact 14m of the change-over switch 14 is connected to thefixed contact 14a, and with the 4.2-V charging voltage V₁ outputted bythe first constant voltage circuit 15, charging of the battery 17 iscarried out (Step S103). And in this event, charging current is detectedby the current detection circuit 20 (Step S104), and judgment is made onwhether the detected charging current value is lower than the specifiedvalue I₁ previously set or not (Step S105).

In this event, if the current exceeds the setting value I₁, the flowreturns to Step S103 and charging with 4.2V charging voltage V₁ iscontinuously carried out. When it is judged that the current is lowerthan the setting value I₁ at Step S105, processing for stopping chargingis carried out (Step S106), the movable contact 14m of the changeoverswitch 14 is changed over to the second fixed contact 14b from the firstfixed contact 14a, and the 4.0-V charging voltage V₂ outputted from thesecond constant voltage circuit 16 is applied to the secondary battery17 (Step S107).

Under th is condition, charging current is detected by the currentdetection circuit 20 (Step S108), the detected charging current value I₂is compared with the previously set specified value I₁ (Step S109), andif the charging current value I₂ is lower than the setting value I₁, theflow returns to Step S108, and current detection is continuously carriedout. If in this current detection, the current value I₂ exceeds thesetting value I₁ (that is, I₂ ≧I₁), the movable contact 14m of thechangeover switch 14 is changed over to the first fixed contact 14a fromthe second fixed contact 14b, the 4.2-V charging voltage V₁ outputted bythe first constant voltage circuit 15 is applied to the secondarybattery 17, and charging is allowed to take place with this 4.2Vcharging voltage V₁ (Step S110). Then, the flow returns to Step S104,and the charging current is detected by the current detection circuit20.

A shown in the flow char t of FIG. 8, controlling the charging operationwith the control circuit 21 allows charging to take place with thecharacteristics shown in FIG. 9. FIG. 9 is a characteristic diagram inwhich charging current/voltage is plotted against the elapsed time, andconstant current charging with the charging current I set as a constantcurrent is carried out from the start of charging until the batteryvoltage attains a specified potential (in this example, the arrangementto carry out constant current charging is omitted), and then, chargingis changed over to constant-voltage charging, and charging takes placewith the 4.2V charging voltage V₁. The execution of this constantvoltage charging causes the battery voltage V to coincide with thecharging voltage V₁, but the charging current I gradually decreases, andthe charging current I becomes the value lower than the previously setcurrent value I₁. The charging current reaching the value lower thanthis current value I₁ means that the secondary battery (lithium ionbattery) is 100% charged.

At the timing when the secondary battery is 100% charged, that is, atthe timing T₁ when the charging current becomes lower than the currentvalue I₁, the changeover switch 14 is changed over from the first fixedcontact 14a to the second fixed contact 14b side, and the chargingvoltage is changed over from 4.2V (V₁) to 4.0V (V₂) (charging voltage V₀shown with a broken line in FIG. 9). The charging voltage becoming 4.0Vin this way prevents the secondary battery 17 from being charged becausethe battery voltage V is 4.2V, and charging current is prevented fromflowing.

Leaving the secondary battery 17 under this condition causes the batteryvoltage V to gradually lower due to self-discharge of the battery (ordischarge to the load 28 connected), but when the voltage lowers to4.0V, the charging voltage, charging current I begins to flow throughthe secondary battery from the charging circuit side. For example, ifthe battery voltage V lowers to 4.0V at the timing T3 of FIG. 9,charging current I₂ is generated, and this charging current I₂ isdetected at the current detection circuit 20. In this event, if thecharging current I₂ is compared with the previously set current value I₁and is greater than the setting value I₁, the charging voltage ischanged over from 4.0V to 4.2V (increase of charging voltage V₀ shownwith a broken line in FIG. 9). By this rise of the charging voltage, thecharging current I further increases and charging takes place. When the100% charged condition is approached by this charging, the chargingcurrent decreases as in the case of the initial charging, and when thecharging current I becomes below the setting value I₁, the chargingvoltage again lowers to 4.0V, and charging operation stops.

The secondary battery is efficiently maintained in the nearly 100%charged condition by carrying out the charging operation of thesecondary battery, the lithium ion battery, in this way. That is, whenthe charging operation is carried out, charging is carried out at 4.2V,the proper charging voltage, until the battery is 100% charged, and atthe same time, after 100% charged, the charging voltage becomes 4.0V,voltage slightly lower than 4.2V, and when the battery voltage V lowersto 4.0V by self-discharge (or discharge to a load), charging voltagerises to 4.2V again, and the operation to 100% charge the battery isrepeatedly carried out. Consequently, after the battery is charged tothe fully charged condition once, every time the remaining batteryvolume lowers to a specified volume, charging to the full charge isrepeated, thereby maintaining the charging condition of the lithium ionbattery constantly to the nearly fully charged condition, and at thesame time, except when this charging to the full charge is carried out,the battery voltage 4.0V slightly lower than that at the time offull-charge of the battery, 4.2V, is applied to the battery, andcharging does not take place until the battery voltage lowers to this4.0V; consequently, the lithium ion battery does not continuously enterthe full-charged condition and deterioration of lithium ion batteryperformance due to the continued full-charged condition can beprevented.

In this example, the charging current I₂ detected at the time ofrecharging is designed to be compared with the current setting value I₁used for charging stop judgment, but it is allowed to compare thecharging current I₂ detected at the time of recharging with the currentvalue set separately from the setting value I₁ and to change over thecharging voltage to 4.2V when the current value exceeding this setcurrent value is detected.

In the example described above, the secondary battery 17 is judged to be100% charged when the charging current becomes lower than the specifiedvalue I₁, but judgment of full charge is allowed to be made in aspecified time passed after the charging current becomes lower than thespecified value I₁. That is, as shown in the flow chart of FIG. 10, whenthe charging current I detected by the current detection circuit 20 inStep S105 becomes lower than the specified value I₁, a timer circuitinside the control circuit 21 is operated (step S111), and when thistimer circuit counts a specified time, processing is allowed to move toStep S107 and to lower the charging voltage from V₁ to V₂. In othersteps of the flow chart of FIG. 10, the processings same as thosedescribed in FIG. 8 take place.

In the example described above, the 100% charged condition is designedto be judged by detection of the charging current, but it may bedesigned to detect the 100% charged condition by detection of batteryvoltage using the voltage detection circuit 18. That is, as shown in theflow chart of FIG. 11, after the charging voltage is set to V₁ in StepS103, it may be designed to detect the battery voltage by the voltagedetection circuit 18 (Step S113), and when the voltage V₁, the voltagevalue corresponding to full-charge, is detected (Step S114), it may bedesigned to allow the processing to move to Step S107 to lower chargingvoltage from V₁ to V₂. In other steps of the flow chart of FIG. 11,processings same as those described in FIG. 8 take place.

When the 100% charged condition is detected by the battery voltage as inthe case of the flow chart of this FIG. 11, it may be designed to judgeas full charge the time when a specified time passes from the time whena specified battery voltage is detected. That is, as shown in the flowchart of FIG. 12, after the charging voltage is set to V₁ in Step S103,battery voltage may be detected by the voltage detection circuit 18(Step S113), and when the voltage V₃, this detected value V₁ detects thevoltage slightly lower than the voltage value corresponding tofull-charge (Step S114), it is judged to be full-charge and theprocessing may move to Step S107 and the charging voltage may be loweredfrom V₁ to V₂. In other steps of the flow chart of FIG. 12, processingssame as those described in FIG. 8 take place.

In the respective flow charts of FIGS. 8, 10, 11, and 12, it may bedesigned for the voltage not to directly lower to the charging voltageV₂ at Step S107 but to detect temperature on the surface or inside ofthe secondary battery 17 and to select voltage values to be lowered inaccord with the detected temperature. That is, in place of Step S107 ofeach drawing, processing of the flow chart of FIG. 17 may be carriedout. The processing of FIG. 17 may be designed to judge whether sometemperature sensor provided in the charging equipment detectstemperature higher than a specified value (here set to 50° C.) assurface temperature, etc. of the secondary battery 17 (Step S131), andif it is 50° C. or lower, to lower the charging voltage to the voltagevalue V₂ described above (for example, 4.0V) (Step S132), and if itexceeds 50° C., to lower the charging voltage to a voltage value (forexample, 3.9V) obtained by subtracting a specified value ΔVα (forexample, 0.1V) from the above-mentioned voltage value V₂ (Step S133),and to move to the next step. Designing the processing in this wayenables the proper setting of the charging voltage corresponding totemperature. In this event, it is necessary to prepare a temperaturesensor and a constant voltage circuit for generating the voltage value(V₂ -ΔVα) in addition to the circuit of FIG. 7.

Now, referring to FIG. 14-FIG. 17, the second embodiment of thisinvention will be described. In this example, the battery temperature isdetected to vary the charging voltage at the time of recharging, and thecharging equipment is configured as shown in FIG. 14. In FIG. 14, partscorresponding to those previously described with reference to FIG. 7 aredenoted by the same reference numerals and their detailed description isomitted.

In this example, the output of the constant current circuit 13 is fed toa movable contact 22m of a change-over switch 22, and the first, thesecond and the third fixed contacts 22a, 22b, and 22c of this changeoverswitch are connected to constant voltage circuits 23, 24, and 25,respectively. Now, the constant voltage circuit 13 is a circuit in which4.2V constant voltage output is obtained, and the constant voltagecircuit 25 is a circuit in which 4.0V constant voltage output isobtained. The outputs of respective constant voltage circuits 23, 24,and 25 are fed to the positive electrode side of the secondary battery17, a lithium ion battery. The current flowing through the currentdetection resistor 19 connected to the negative electrode side of thissecondary battery 17 is detected with the current detection circuit 20,and the detection data of the current value is compared with the currentvalue I₁ set for the standard by a control circuit 26, and based on thecomparison results, the changeover switch 22 is controlled. The insidetemperature or surface temperature of the secondary battery 17 connectedto this charging equipment or temperature in the vicinity of thesecondary battery 17 is designed to be detected by a temperature sensor27, and the data on the detected temperature is designed to be suppliedto the control circuit 26, and based on the judgment whether thedetected temperature is the set temperature Ta or higher, thechange-over condition in controlling the changeover switch 22 is varied.For this set temperature Ta, for example, 50° C. is designated.

Other portions are configured in the same manner as in the case of thecharging equipment shown in FIG. 7. Though it is not illustrated, in thecase of this charging equipment, a load circuit may be connected to thesecondary battery.

Now, referring to a flow chart of FIG. 15, operation when charging iscarried out by the charging equipment of this example will be described.In the flow chart of FIG. 15, the same processing in the flow chart asshown in FIG. 8 takes place up to Step S109 (that is, step in which thecharging current value I₂ detected after the battery is 100% chargedonce is compared with the setting value I₁) and the description thereofwill be omitted. However, the charging voltage V₁ set in Step S103 is4.2V voltage by the constant voltage circuit 23 (that is, the movablecontact 22m of the changeover switch 22 is connected to the first fixedcontact 22a), and the charging voltage V₂ set in Step S107 is 4.0Vvoltage by the constant voltage circuit 25 (that is, the movable contact22m of the changeover switch 22 is connected to the third fixed contact22c).

When the comparison in Step S109 indicates that the detected chargingcurrent value I₂ is greater than the setting value I₁ (that is I₂ ≧I₁)the detected temperature of the temperature sensor 27 is judged, andjudgment is made on whether the detected temperature is higher than theset temperature Ta (for example, 50° C.) (Step S121). In this event, ifthe detected temperature is higher than the set temperature Ta, themovable contact 22m of the changeover switch 22 is changed over from thethird fixed contact 22c to the second fixed contact 22b, and 4.1Vcharging voltage outputted by the second constant voltage circuit 24(this charging voltage is designated to V₁ -ΔVα) is applied to thesecondary battery 17, and charging is carried out with this 4.1Vcharging voltage V₁ -ΔVα (Step S122). Then, the processing returns toStep S104 where charging current is detected by the current detectioncircuit 20.

If the detected temperature is less than the set temperature Ta in StepS121, the movable contact 22m of the changeover switch 22 is changedover from the third fixed contact 22c of the changeover switch 22 to thefirst fixed contact 22a, and 4.2V charging voltage V₁ outputted by thefirst constant voltage circuit 23 is applied to the secondary battery17, and charging is carried out with this 4.2V charging voltage V₁ (StepS123). Then, the processing returns to Step S104 where the chargingcurrent is detected by the current detection circuit 20.

As shown in the flow chart of FIG. 15, controlling the chargingoperation by the control circuit 26 allows charging to take place withthe characteristics shown in FIG. 16. FIG. 16 is a characteristicdiagram with charging current/voltage plotted against the elapsed time,indicating that charging is carried out at 4.2V charging voltage V₁ onceconstant voltage charging is established after the start of charging.Execution of this constant voltage charging allows the battery voltage Vto coincide with the charging voltage V₁ but the charging current Igradually decreases, and when the charging current I attains the presetcurrent value I₁ or lower, the secondary battery (lithium ion battery)is 100% charged. At the timing T₁ with the battery 100% charged, thechangeover switch 12 is changed over from the first fixed contact 12a tothe third fixed contact 12c side, and the charging voltage is changedover from 4.2V (V₁) to 4.0V (V₂) (lowering of charging voltage V₀ shownwith a broken line in FIG. 16). By the charging voltage attaining 4.0Vin this way, charging to the secondary battery 7 is not carried outbecause the battery voltage V is 4.2V, and the charging current isprevented from flowing. Up to this point, the condition is exactly sameas that described in connection with FIG. 9.

If the secondary battery 17 is left as it is under this condition, thebattery voltage V gradually lowers due to the self-discharge (ordischarge to the load connected), but when it lowers to 4.0V, thecharging voltage (timing T₂ in FIG. 16), charging current I₂ starts toflow from the charging circuit side to the secondary battery 17. Andthis charging current I₂ is detected by the current detection circuit 20and compared with the setting value I₁ and if it is the setting value I₁or higher, processing to raise the charging voltage is carried out, butdepending on whether or not the detected temperature of the temperaturesensor 27 in this event is the set temperature Ta or higher, either V₁(4.2V) or V₂ -ΔVα (4.1V) is selected for the changed-over chargingvoltage.

That is, if the detected temperature in this event is the settemperature Ta or higher, 4.1V is selected for the charging voltage, andthe battery is charged with this 4.1V charging voltage until the batteryvoltage reaches 4.1V (the condition of battery voltage Va shown in FIG.16). Because this condition in which the battery voltage is 4.1Vprovides a potential slightly lower than the battery voltage 4.2V whenthe battery is 100% charged, charging stops with the battery chargedwith a volume slightly lower than 100% (for example, 90%). And if thedetected temperature is less than the set temperature Ta, 4.2V isselected for the charging voltage, and with this 4.2V charging voltage,the battery voltage becomes 4.2V and the battery is 100% charged(condition of battery voltage Vb shown in FIG. 16).

By varying the charging voltage for re-charging after fully charged inthis way in accord with the battery or its surrounding temperature, thebattery protection is carried out when temperature is high. That is,when the temperature is high, the lithiumion battery has a disadvantagein which characteristic deterioration (that is, reduction of chargingcapacity) when 100% charged occurs more quickly than at the normal time,and it is not preferable to charge the battery to 100%. Now, in the caseof this example, when the battery temperature is high, charging isdesigned to be stopped right before 100% charging takes place, therebypreventing characteristic deterioration due to 100% charging at hightemperatures. Because when the battery temperature is not high, thebattery is designed to be 100% charged, the battery is charged to thepoint in which the capacity of the secondary battery is able to beutilized to the maximum when no protection due to temperature isrequired, enabling highly efficient charging. With respect to thecharging operation when the temperature is lower than the settemperature Ta, exactly same charging operation of one embodimentdescribed in connection with FIG. 9 takes place, providing the similareffects as in the case of the one embodiment.

In the example described in connection with FIG. 14-FIG. 16, thecharging voltage at the time of re-charging is changed over between twotypes based on the judgment on whether or not the temperature is the settemperature Ta or higher, but charging voltage may be controlled morefinely based on the results of temperature detection more finely carriedout. For example, in place of the temperature judgment at Step S121 inthe flow chart of FIG. 15 and setting of charging voltage at Steps S122,S123 based on the judgment, temperature may be judged in two stages asshown in the flow chart of FIG. 17, and the charging voltage at the timeof re-charging may be changed over in three stages.

That is, as shown in the flow chart of FIG. 17, first of all, judgmentis made on whether or not the temperature detected by the temperaturesensor 27 is 50° C. or higher (Step S124), and if it is higher than 50°C., further judgment is made on whether or not the temperature is 60° C.or higher (Step S125). And if it is judged to be 60° C. or higher, [V₂-2ΔVα] is set for the charging voltage (Step S126). In this event, letV₁ 4.2V and ΔVα be 0.1V, 4.0V is set (if V₂ is 4.0V, charging voltagewill not vary).

If the temperature is judged to be less than 60° C. at Step S125, [V₁-ΔVα] is set as charging voltage (Step S127). Here, assuming the valuesof the V₁ and ΔVα, 4.1V is set.

When the temperature is judged to be less than 50° C. at Step S124, V₁is set as charging voltage (Step S128). Here, assuming theabove-mentioned value for V₁, 4.2V is set.

Controlling the voltage more finely in accord with the temperature inthis way achieves an effect in that protection of the secondary batteryby temperature is able to be carried out more accurately. In addition tochanging temperature stepwise in this way, the voltage value at the timeof re-charging may be continuously varied in accord with the detectedtemperature.

With respect to specific configuration of the temperature sensor 27 fordetecting temperature of the secondary battery 7, no particulardescription is made here, but temperature sensors of variousconfigurations may be applied. For example, the surface temperature ofthe secondary battery may be detected by an infrared sensor, or theinside temperature may be detected by a terminal for temperaturedetection equipped to the secondary battery, and in addition, using somekind of temperature detection elements, temperature in the vicinity ofthe mounting portion of the secondary battery may be detected.

Now referring to FIG. 18 and FIG. 19, the third embodiment according tothis invention will be described.

FIG. 18 is a block diagram showing an arrangement of the chargingequipment of this example, in which AC power supply from a commercial ACpower supply 41 is fed to a rectifier circuit 42 comprising a diodebridge to provide a DC power supply. This DC power supply is fed to aprimary side control circuit 43, and specified processing is carried outat this primary-side control circuit 43, and the then is fed to aprimary-side winding 44a of a switching transformer 44. And on asecondary-side winding 44b of the switching transformer 44, low-voltageDC power supply converted to specified low voltage is obtained. In thisevent, on the primary side of the switching transformer 44, an auxiliarywinding 44c is provided for controlling the switching condition. To theprimary-side control circuit 43, a control signal is supplied from acharging control circuit 50 on the secondary side later described via aphotocoupler 52, and the output voltage is controlled in accord withthis control signal.

One end of the secondary winding 44b of this switching transformer 44 isconnected to the anode of a switching diode 45, and the cathode of thisdiode 45 an the other end of the secondary winding 44b are connected bya switching capacitor 46 to provide a DC low-voltage power supply of aspecified voltage.

The anode of the diode 45 from which the low-voltage DC power supply isobtained is connected to one end (positive electrode) of a secondarybattery (here, lithium ion battery is used for the secondary battery) 47loaded on this charging equipment, and the other end of this secondarybattery 47 (negative electrode) is connected to the other end of thesecondary winding 44 of the switching transformer 44 via the source andthe drain of a field-effect transistor (FET) 48, a switching means forcharging control. In this case, the connecting direction across thesource and the drain of the field-effect transistor 48 is such that thecurrent flows from the secondary battery 47 to the other end side of thesecondary winding 44b when this transistor 48 conducts, and the currentflowing from this secondary battery 47 to the other end side of thesecondary winding 44b is restricted when it does not conduct. Across thesource and the drain of this field-effect transistor 48, a parasiticdiode 49 is generated in which the current flows in the directionreversal to the direction to control the current flow (that is, thedirection in which the current flows from the other end side of thesecondary winding 44b to the negative electrode of the secondary battery47).

And for a circuit to control the gate of this transistor 48, thecharging control circuit 50 is provided. The charging control circuit 50comprises an integrated circuit and is connected in such a manner forthe signal obtained on the secondary side of the switching transformer44 is supplied as a power supply. That is, the cathode of the diode 45and the other end side of the secondary winding 44b are connected to thecharging control circuit 50 respectively. From this charging controlcircuit 50 to the gate of the transistor 48, the switching controlsignal is supplied to control the current flow as described above (thatis, control of conduction and nonconduction), and at the same time whenit is brought to the nonconducting state, the impedance across thesource and the drain is designed to be controlled to be high.

In the present example, a voltage detection circuit 51 is provided fordetecting the potential across one end and the other end of the chargingcurrent path of the field effect transistor 48, that is, the potentialacross the source and the drain, and the data of the potential acrossthe source and the drain detected by this detection circuit 51 issupplied to the charging control circuit 50.

The charging control circuit 50, based on the detection data of thisvoltage detection circuit 51, controls the condition of the transistor48. The charging control circuit 50 is designed to supply the voltagecontrol signal (that is, the signal which varies in proportion to thevoltage value to control) to a light emitting diode 52a comprising thephotocoupler 52. A light receiving element 52b for receiving light fromthe light emitting diode 52a of this photocoupler 52 is connected to theprimary side control circuit 43, so that the voltage control signaloutputted by the charging control circuit 50 can be transmitted to theprimary side control circuit 43. The primary side control circuit 43,based on this voltage control signal, controls the voltage of the powersupply obtained for the secondary winding 44b of the switchingtransformer 44.

Now referring to the flow chart of FIG. 19, operation when the secondarybattery 47 is charged with the charging equipment of the configurationof FIG. 18 is described with special emphasis on the pre-chargingoperation when charging begins.

When the secondary battery 47, the lithium ion battery, is charged,processing called pre-charging is carried out, and then, processing fordetecting the condition of the secondary battery 47 is carried out (StepS201). For pre-charging processing in the case of this example, first,by the control signal to be supplied from the charging control circuit50 to the gate of the field effect transistor 48, the impedance acrossthe source and drain of this transistor 48 is brought into the highstate. In the case of this example, for the secondary battery 47, theone with the battery voltage of 4.2V when fully charged is used, and atthe time of pre-charging, the voltage of the power supply obtained inthe secondary winding 44b of the switching transformer 44 (hereinaftersimply called input power supply) is set to 4.2V or a voltage slightlylower than 4.2V.

Under this condition, the voltage across the source and the drain of thefield effect transistor 48 is detected in the voltage detection circuit51 (Step S202). And the detected voltage is judged by the chargingcontrol circuit 50 to judge whether or not the voltage is the standardvoltage or higher previously set to the charging control circuit 50(Step S203). And if the voltage is the standard voltage or higher,processing to lower the input power supply voltage by the voltagecontrol signal supplied from the charging control circuit 50 to theprimary side control circuit 43 via the photocoupler 52 (Step S204), andpre-charging operation is allowed to continue under this condition (StepS205).

When the voltage detected by the voltage detection circuit 51 is lessthan the standard voltage, pre-charging operation is allowed to continueat the input power supply voltage as it is.

After this pre-charging is started, the condition of the secondarybattery 47 (such as battery voltage, etc.) is detected, and when thebattery voltage etc. is brought to a specified state, the high impedancestate is changed to the conducting state across the source and the drainof the transistor 48, and the secondary battery 47 is charged with aninput power supply of comparatively large current (e.g. 1A), allowing itto carry out so-called rapid charging.

As described above, according to the charging equipment of this example,allowing the charging current with the field effect transistor 48, aswitching means for controlling the start of charging, held in thehigh-impedance state enables pre-charging by a small current, and thecondition of the secondary battery 47 mounted is able to be accuratelydetected. And pre-charging under the high-impedance state with the powersupply voltage lowered to allow the charging current to flow achievespre-charging with loss reduced at the field effect transistor 48,thereby enabling highly efficient pre-charging.

Now referring to FIG. 20 and FIG. 21, the fourth embodiment according tothe present invention is described. In FIG. 20 showing the configurationof the charging equipment of the fourth embodiment, parts similar to orcorresponding to those previously described with reference to FIG. 18which shows the configuration of the third embodiment are denoted by thesame reference numerals, and their detailed description is omitted.

Turning now to the configuration of the fourth embodiment, in thisexample, as shown in FIG. 20, the anode of the diode 45 from which thelow-voltage DC power supply is obtained is connected to one end(positive electrode) of the secondary battery 47 (lithium ion battery)loaded on this charging equipment, and the other end (negativeelectrode) of this secondary battery 47 is connected to the other end ofthe secondary winding 44b of the switching transformer 44 via across thesource and the drain of the field-effect transistor (FET) 48, aswitching means for charging control. In this case, the connectingdirection across the source and the drain of the field-effect transistor48 is such that the current flows from the secondary battery 47 to theother end side of the secondary winding 44b when this transistor 48conducts, and the current flowing from this secondary battery 47 to theother end side of the secondary winding 44b is restricted when it doesnot conduct.

And for a circuit to control the gate of this transistor 48, a chargingcontrol circuit 54 is provided. The charging control circuit 54comprises an integrated circuit and is connected in such a manner forthe signal obtained on the secondary side of the switching transformer44 is supplied as a power supply. That is, the cathode of the diode 45and the other end side of the secondary winding 44b are connected to thecharging control circuit 54 respectively. From this charging controlcircuit 54 to the gate of the transistor 48, the switching controlsignal is supplied to control the current flow as described above (thatis, control of conduction and nonconduction), and at the same time whenit is brought to the nonconducting state, the impedance across thesource and the drain is designed to be controlled to be high.

In the present example, a voltage detection circuit 53 is provided fordetecting the battery voltage, that is, the potential across oneelectrode and the other electrode of the secondary battery 47 mounted,and the data of the battery voltage detected by this detection circuit53 is supplied to the charging control circuit 54.

In the charging control circuit 54, based on the detection data of thisvoltage detection circuit 53, the condition of the transistor 48 iscontrolled. The charging control circuit 54 is designed to supply thevoltage control signal to the primary side control circuit 43 via thephotocoupler 52. In the primary side control circuit 43, based on thisvoltage control signal, the voltage of the power supply obtained for thesecondary winding 44b of the switching transformer 44 is designed to becontrolled. Other portions are configured in the same manner as in thecase of the charging equipment shown in FIG. 18.

Now referring to the flow chart of FIG. 21, operation when the secondarybattery 47 is charged with the charging equipment of the configurationof FIG. 20 is described with special emphasis on the pre-chargingoperation when charging begins.

When the secondary battery 47, the lithium ion battery, is charged inthe circuit of this example, processing for detecting the batteryvoltage by the voltage detection circuit 53 with the impedance acrossthe source and the drain of this transistor 48 held in the high state bythe control signal supplied from the charging control 54 to the gate ofthe filed effect transistor 48 is carried out (Step S211).

And the detected voltage is judged by the charging control circuit 54 tojudge whether or not the voltage is 0V or the value close to 0V (StepS212). And if the voltage is 0V or the value close to 0V, processing tolower the input power supply voltage is carried out by the voltagecontrol signal supplied from the charging control circuit 54 to theprimary side control circuit 43 via the photocoupler 52 (Step S213), andpre-charging operation is allowed to continue under this condition (StepS214).

When the voltage detected by the voltage detection circuit 53 is not thevalue close to 0V, processing to continue pre-charging operation iscarried out at the input power supply voltage as it is.

After this pre-charging is started, the condition of the secondarybattery 47 (such as battery voltage, etc.) is detected, and when thebattery voltage etc. is brought to a specified state, the high impedancestate is changed to the conducting state across the source and the drainof the transistor 48, and the secondary battery 47 is charged with aninput power supply of comparatively large current (e.g. 1A), allowing itto carry out so-called rapid charging.

As described above, according to the charging equipment of this example,similar to the third embodiment described above, the charging currentwith the field effect transistor 48, a switching means for controllingthe start of charging is, held in the high-impedance state which enablespre-charging by a small current, and the condition of the secondarybattery 47 mounted is able to be accurately detected. And pre-chargingunder the high-impedance state with the power supply voltage lowered toallow the charging current to flow achieves pre-charging with lossreduced at the field effect transistor 48, thereby enabling highlyefficient pre-charging.

Now, referring to the flow chart of FIG. 22, the fifth embodiment of thepresent invention is described. In the case of the fifth embodiment, thesecondary battery (lithium ion battery) is charged by the chargingequipment of the circuit configuration of the third embodiment mentionedabove, and processing of pre-charging by the control of the chargingcontrol circuit 50 is carried out as shown in the flow chart of FIG. 22.

That is, at the start of charging, pre-charging operation is startedwith the field effect transistor 48, a switching means for controllingthe start of charging brought into the high state (Step S221). In thisevent, the charging control circuit 50 is controlled to bring the powersupply voltage obtained in the secondary winding 44b of the switchingtransformer 44 to a low voltage (Step S222). The voltage in this eventshould be the minimum voltage that can operate the charging controlcircuit 50 formed with integrated circuits (for example, 3.0V) or thevoltage slightly higher than that.

Under this condition, pre-charging is carried out (Step S223), and thepotential across one end and the other end of the transistor 48 in thehigh impedance state is detected by the voltage detection circuit 51(Step S224), and at the same time, the time in the charging controlcircuit 50 is operated (Step S231). And it is judged whether or not thedetected voltage is the standard voltage or higher (Step S225). And ifthe voltage is the standard voltage or lower, the battery voltage isjudged to be low, and processing is returned to pre-charging at StepS223.

When it is judged to be the standard voltage or higher at Step S225,after the timer operated at Step S231 is stopped (Step S226), and thefield effect transistor 48 is brought into the conducting state toincrease the charging current, and rapid charging is carried out (StepS227).

And if the condition in which the voltage is detected to be lower thanthe standard voltage at Step S225 continues, it must be determinedwhether or not it has passed 1 hour since the timer began to be operatedat Step S231 (Step S232), and if one hour has passed, it shall be judgedthat something wrong occurs in the secondary battery 47 at this time,and the transistor 48 shall be brought into the nonconducting state tostop charging (Step S233).

Carrying out processing at the start of charging in this way enables thedetection of the condition of the secondary battery mounted with thefield effect transistor, a switching means for controlling the charging,brought into the high impedance state before rapid charging, and highlyefficient detection processing of the battery condition is achievedsimilar to the third embodiment. In this example, lowering the outputvoltage of the power supply circuit (switching power supply) at the timeof precharging under the condition for detecting the battery conditionto the minimum voltage at which the charging control circuit 50, theintegrated circuit, can be operated carries out pre-charging at theminimum voltage under the condition that enables the control of chargingby the charging control circuit 50, and precharging is enabled under thecondition with the lowest voltage applied to the secondary battery.Consequently, it is possible to detect the condition of the secondarybattery with the minimum burden to the secondary battery or the circuit,thereby enabling the detection of the secondary battery under thefavorable condition.

In this fifth embodiment, the potential across one end and the other endof the field effect transistor 48 described in the third embodiment isdetected and is applied to the configuration in which the batterycondition is detected, but it is possible to apply to the configurationin which the battery voltage is detected described in the fourthembodiment. That is, in the configuration of FIG. 20 described in thefourth embodiment, the power supply voltage at the time of prechargingmay be brought to the minimum voltage that can operate the chargingcontrol circuit 54.

Now referring to FIG. 23-FIG. 25, the sixth embodiment of the presentinvention is described. In the case of this sixth embodiment, thesecondary battery (lithium ion battery) is charged by the chargingequipment of the circuit shown in FIG. 23. In FIG. 23 showing theconfiguration of the charging equipment of the sixth embodiment, partscorresponding to those previously described with reference to FIG. 18and FIG. 20 which show a configuration of the fourth embodiment aredenoted by the same reference numerals, and their detailed descriptionis omitted.

Referring to FIG. 23, the charging equipment of this example isdescribed. The circuit of FIG. 23 has the primary side of the switchingtransformer 44 omitted, and the power supply output as the switchingpower supply is obtained by the diode 45 and the capacitor 46 connectedto the secondary side winding 44b. The cathode of the diode 45 which isthe power output of one electrode is connected to the positive electrodeside of the secondary battery (lithium ion battery) 47 mounted to thischarging equipment, and at the same time, the negative electrode side ofthis secondary battery 47 is connected to the other end side (the sideto which diode 45 is not connected) of the secondary winding 44b via thefield effect transistor 48 which is the switching means for chargingcontrol.

And a voltage detection/charging control circuit 55 for detecting thevoltage across the terminals of the secondary battery 47 and controllingcharging in accord with the detected potential is provided. To thisvoltage detection/charging control circuit 55, one and the otherterminals of this battery 47 are connected to detect the voltage acrossterminals of the secondary battery 47 as well as to supply the output ofthe switching power supply. And based on the detected battery voltage,control is carried out on the gate of the field effect transistor 48, ondetermining which state should be selected for this transistor 48, fromthree conditions of conducting, nonconducting, and high-impedance, andon charging. In FIG. 23, the parasitic diode of the field effecttransistor 48 is omitted. To this point, the configuration is same asthat of the fourth embodiment described above.

In this example, the voltage control of the switching power supply bythe voltage detection/charging control circuit 55 is carried out inproportion to the battery voltage at that time. To describe theconfiguration, using the series circuit of resistors 56, 57, one end andthe other end from which the output of the switching power are obtainedare connected, and the connection middle point of these resistors 56, 57is connected to the base of an NPN type transistor 58. The cathode ofthe diode 45 is connected to the collector of the transistor 48 via thelight emitting diode 52a, of the photo coupler 52 and the other side ofthe secondary winding 44b is connected to the emitter of the transistor58 via a zener diode 59.

Using the series circuit of resistors 60, 61, the cathode of diode 45and the voltage control terminal of the voltage detection/chargingcontrol circuit 55 are connected, and the connection middle point of theresistors 60, 61 is connected to the base of a PNP type transistor 62.The cathode of the diode 45 is connected to the emitter of thistransistor 62, and the collector of this transistor 62 is connected tothe base of the transistor 58 via a resistor 63.

In this kind of circuit configuration, varying the voltage value of thevoltage control signal outputted from the voltage control terminal inproportion to the battery voltage detected by the voltagedetection/charging control circuit 55 at the time of precharging variesthe voltage control condition at the control circuit on the primary sideof the switching power supply not illustrated, and the voltage of thepower supply supplied to the secondary battery 47 is varied.

Now, processing at the time of precharging in this example is describedreferring to the flow chart of FIG. 24 and the voltage characteristicdiagram of FIG. 25. First of all, the transistor 48 is brought into thehigh impedance state, the power supply voltage Va is brought to theminimum voltage (for example, the minimum voltage that can operate thevoltage detection/charging control circuit 55), and prechargingoperation is started (Step S241). And the battery voltage Vb is detected(Step S242). In this event, the battery 47 is gradually charged by thisprecharging, and as shown in FIG. 8, the battery voltage VA graduallyrises. At this point, control for increasing the power supply voltage VAis carried out as shown in FIG. 25 in proportion to the increase ofvoltage by the control of the voltage detection/charging control circuit55 (Step S243).

And whether or not the battery voltage VB attains the predeterminedstandard voltage V₂₁ or higher is judged (Step S244), and if it is lessthan the standard voltage V₂₁, control is carried out for increasingpower supply voltage in proportion to the battery voltage at Step S242and S243. And if it is judged that the voltage attains the standardvoltage V₂₁ or higher at Step S224, the transistor 48 is changed fromthe high-impedance state to the conducting state to increase thecharging current, and rapid charging is started with the power supply VAused for the voltage V₂₂ for rapid charging (Step S245).

Carrying out control at the time of precharging in this way can keep thepower applied to the field effect transistor 48 constantly to nearlysame level during precharging, and the condition of the field effecttransistor 48, the switching means, can be maintained in the favorablecondition.

In this example, the battery voltage is designed to be detected duringprecharging, but instead, as shown in the third embodiment, the voltageacross the source and the drain of the field effect transistor 48 may bedesigned to be detected.

Now referring to FIG. 26 and FIG. 27, the seventh embodiment of thepresent invention is described. In the case of this seventh embodiment,the secondary battery (lithium ion battery) is charged by the chargingequipment of the circuit shown in FIG. 26. In FIG. 26 showing theconfiguration of the charging equipment of the seventh embodiment, partscorresponding to those previously described with reference to FIG. 18,FIG. 20, and FIG. 23 which show a configuration of the third, fourth,and sixth embodiments are denoted by the same reference numerals, andtheir detailed description is omitted.

Referring to FIG. 26, the charging equipment of this example isdescribed. The circuit of FIG. 26 has the primary side of the switchingtransformer 44 omitted as in the case of the circuit of FIG. 23, and thepower supply output as the switching power supply is obtained by thediode 45 and the capacitor 46 connected to the secondary side winding44b. The cathode of the diode 45 which is the power output of oneelectrode is connected to the positive electrode side of the secondarybattery (lithium ion battery) 47 mounted to this charging equipment, andat the same time, the negative electrode side of this secondary battery47 is connected to the other end side (the side to which diode 45 is notconnected) of the secondary winding 44b via the field effect transistor48 which is the switching means for charging control.

And the voltage detection/charging control circuit 55 for detecting thevoltage across the terminals of the secondary battery 47 and controllingcharging in accord with the detected potential is provided, and based onthe detected battery voltage, control is carried out on the gate of thefield effect transistor 48, on determining which state should beselected for this transistor 48, from three conditions, conducting,nonconducting, and high-impedance, and on charging. To this point, theconfiguration is same as that of the charging equipment of the sixthembodiment shown in FIG. 23.

In this example, control is designed to be carried out in such a mannerthat the voltage of the switching power supply by the voltagedetection/charging control circuit 55 is varied in a plurality of stagesin proportion to the battery voltage at this time. To describe theconfiguration, using the series circuit of resistors 56, 57, one end andthe other end from which the output of the switching power are obtainedare connected, and the connection middle point of these resistors 56, 57is connected to the base of the NPN type transistor 58. The cathode ofthe diode 45 is connected to the collector of the transistor 48 via thelight emitting diode 52a of the photo coupler 52, and the other side ofthe secondary winding 44b is connected to the emitter of the transistor58 via the zener diode 59.

To the cathode of diode 45, one end of the resistor 60 is connected, andthe other terminal of this resistor 60 is connected to the base of thePNP type transistor 62. The cathode of the diode 45 is connected to theemitter of this transistor 62, and the collector of this transistor 62is connected to the base of the transistor 58 via the resistor 63.

And zener diodes 64, 65, 66 with different voltage characteristics,respectively, are prepared, and the cathodes of these three zener diodes64, 65, 66 are connected to the connection point between the resistor 56and the base of the transistor 62. The anode of each of zener diodes 64,65, 66 is connected to the other end side of the secondary wiring 44bvia a change over switch 67, and depending on the change-over conditionof the changeover switch 67, only the anode of either one of the zenerdiodes 64, 65, 66 is connected to the other end side of the secondarywiring 44b. The change-over of this changeover switch 67 is controlledby the voltage control signal voltage outputted from the voltage controlterminal of the voltage detection/charging control circuit 55.

In this kind of circuit configuration, varying the voltage value of thevoltage control signal outputted from the voltage control terminal in aplurality of stages in proportion to the battery voltage detected by thevoltage detection/charging control circuit 55 at the time of prechargingvaries in a plurality of stages the voltage control condition at thecontrol circuit on the primary side of the switching power supply notillustrated, and the voltage of the power supply supplied to thesecondary battery 47 is varied in a plurality of stages.

Now, processing at the time of precharging in this example is describedreferring to the voltage characteristic diagram of FIG. 27. First ofall, the transistor 48 is brought into the high impedance state, thepower supply voltage VA is brought to the minimum voltage (for example,the minimum voltage that can operate the voltage detection/chargingcontrol circuit 55), and precharging operation is started. That is, azener diode whose voltage becomes the minimum by the changeover switch67 (for example, zener diode 64) is connected. And the battery 47 isgradually charged by this precharging, and as shown in FIG. 27, thebattery voltage VB gradually rises. At this point, when the batteryvoltage VB rises to a certain value, the changeover switch 67 is changedover by the control of the voltage detection/charging control circuit55, and the power supply voltage VA is increased by one step. And whenthe battery voltage VB is further increased to a certain value, thechangeover switch 67 is changed over by the control of the voltagedetection/charge control circuit 55, and the power supply voltage VA isincreased by one more step.

And when the battery voltage VB attains the predetermined standardvoltage V₂₁ or higher, the transistor 48 is changed from thehigh-impedance state to the conducting state to increase the chargingcurrent, and rapid charging is started with the power supply VA used forthe voltage V₂₂ for rapid charging.

Carrying out control at the time of precharging in this way can keep thepower applied to the field effect transistor 48 constantly to nearlysame level during precharging, and the condition of the field effecttransistor 48, the switching means, can be maintained in the favorablecondition. In this event, in the case of this seventh embodiment,control of the power supply voltage is carried out in a plurality ofstages, and control is able to be effected with a simpler configurationthan in the case of sixth embodiment in which the power supply voltageis controlled nearly continuously.

In the case of this seventh embodiment as well, the battery voltage isdesigned to be detected during precharging, but instead, as shown in thethird embodiment, the voltage across the source and the drain of thefield effect transistor 48 may be designed to be detected.

In this seventh embodiment, the power supply voltage during prechargingis designed to be varied in three stages, but it may be varied in twostages or more than three stages.

Now referring to FIG. 28, the eighth embodiment of the present inventionis described. In the case of this eighth embodiment, the secondarybattery (lithium ion battery) 33 is charged by the charging equipment ofa circuit shown in FIG. 28.

Referring to FIG. 28, the charging equipment of this example isdescribed. FIG. 28 schematically shows the supply source of the powersupply voltage in a block form, where two types of power supply areprepared: a first constant voltage source 71 for generating the voltageduring precharging and a second constant voltage source 72 forgenerating the voltage during rapid charging. In this event, the outputvoltage of the first constant voltage source 71 should be the voltagelower than the minimum required voltage for operating a charging controlcircuit 75 later described. The outputs of these two constant voltagesources 71, 72 are selectively supplied to the positive electrode sideof the secondary battery (lithium ion battery) 33 by the change overswitch 73. In this event, the change-over of the change over switch 73is controlled by the charging control circuit 75.

And across the negative side of the secondary battery 33 and theconstant voltage sources 71, 72, a field effect transistor 48 as aswitching means for controlling charging is connected. The field effecttransistor 48 is controlled by the charging control circuit 75 composedof integrated circuits, and is controlled in the three states:conducting, nonconducting, and high-impedance. And the detection signalof the voltage detection circuit 77 for detecting the battery voltage ofthe secondary battery 33 is designed to be supplied to the chargingcontrol circuit 75.

For the power supply feeding path of the charging control circuit 75,the power supply selected by the switch 73 is designed to be suppliedvia a diode 74. And in parallel to the power supply feeding path of thischarging control circuit 75, a capacitor 76 with comparatively largecapacity is connected.

For control of charging by the charging control circuit 75, in carryingout precharging, the transistor 48 is brought to the high-impedancestate, and then the switch 73 is changed over as required to change overthe first constant voltage source 71 and the second constant voltagesource 72 as required. The change-over frequency should be such that thecondition in which a sufficient volume of charge is accumulated in thecapacitor 76 is maintained.

At the time of rapid charging, the transistor 48 is brought to theconducting state, and the output of the second constant voltage source72 is continuously supplied to the secondary battery 33. Thisprecharging is changed over to and from rapid charging based on thedetection of the battery voltage by the voltage detection circuit 77.

Controlling in this way is unable to secure a required voltage foroperating the charging control circuit 75 under the condition in whichthe output of the first constant voltage source 71 supplied to thesecondary battery 33 during precharging, but while the power supply isfed from the second constant voltage source 72 (the voltage of thispower supply is the voltage big enough to operate the charging controlcircuit 75), the capacitor 76 is charged. Consequently, while the outputof the first constant voltage source is being supplied, the voltageenough to operate the charging control circuit 75 is obtained by thecharge charged to the capacitor 76, and proper precharging control iscarried out by the charging control circuit 75.

Because the power supply voltage during precharging is able to be madelower than the voltage required for operating the circuit in thecharging equipment, the voltage of the power supply fed to the secondarybattery 33 during precharging can be made extremely low, and favorableprecharging can be achieved by extremely low voltage. That is, becausethe power supply voltage fed to the secondary battery 33 can be made lowduring precharging, even when there is any trouble in the secondarybattery 33 due to some factor (for example, when shorting occurs acrossterminals), damages on the charging circuit side attributed to it can besuppressed to the minimum.

In the case of this eighth embodiment, two constant voltage sources areprovided for changing over between the two, but as described in otherembodiments, it may be configured to vary the power supply voltage bythe control of the primary side of the switching power supply or others.In the case of the sixth embodiment as well, the battery condition isdesigned to be detected by detection of the battery voltage, but it maybe configured to detect the potential across one end and the other endof the switching means (field effect transistor 48).

Now referring to FIG. 29-FIG. 33, the ninth embodiment of the presentinvention is described.

FIG. 29 is a block diagram showing the configuration of the chargingequipment applied to this embodiment, and using the charging equipmentof the configuration shown in FIG. 29, charging is carried out.

First of all, the configuration of the charging equipment shown in FIG.29 is described, where AC power supply is supplied from a commercial ACpower supply 81 to a transformer/rectifier circuit 82 to provide DClow-voltage power supply. And this DC low-voltage power supply issupplied to a constant current circuit 83 to provide an output of aconstant current. And this constant-current output is supplied to aconstant voltage circuit 84 to obtain an output of a constant voltage.In this case, this constant voltage circuit 84 is designed to set 4.2Vconstant voltage output and 4.0V constant voltage output. For thisoutput voltage, either 4.2V or 4.0V is designed to be selected by thecontrol of a control circuit 87 later described.

On the positive electrode side of a secondary battery 85 mounted to thischarging equipment, the output voltage of the constant voltage circuit84 is supplied. In this event, in this example, a lithium ion battery isused for the secondary battery 85. The lithium ion battery used heremust provide characteristics in which the battery voltage is 4.2V whenthe battery is 100% charged (fully charged). Then, the potentialdifference between the positive electrode side and the negativeelectrode side of this secondary battery 85 is detected with a voltagedetection circuit 86. The data of voltage values detected in thisvoltage detection circuit 86 is supplied to a control circuit 87.

The negative electrode side of the secondary battery 85 is connected tothe transformer/rectifier circuit 82 via a current detection resistor 88to form a charging circuit of the secondary battery 85. Based on thepotential difference between one end and the other end of the currentdetection resistor 88, the current flowing through the resistor 88 isdetected by a current detection circuit 89. The current value detectedby this current detection circuit 89 corresponds to the charging currentsupplied to the secondary battery 85. The data of current valuesdetected by the current detection circuit 89 is supplied to the controlcircuit 87. This control circuit 87 is a circuit composed by amicrocomputer with integrated circuits for controlling the chargingoperation, and based on the data of the battery voltage detected by thevoltage detection circuit 86 and the data of current values detected bythe current detection circuit 89, the supply from the constant voltagecircuit 84 to the secondary battery 85 of the charging power supply iscontrolled. The control circuit 87 of this example has a timer circuit(not illustrated) built in so that the passage of a predetermined timeis designed to be judged.

By the way, there is a case in which a load circuit 90 may be connectedto the secondary battery 85.

Now, referring to the flow chart of FIG. 30, charging processing of theninth embodiment in which the secondary battery (lithium ion battery) ischarged using the charging equipment shown in FIG. 29 will be described.

The charging control of this example is carried out based on the controlof the control circuit 87, and when the charging operation begins andthe battery is charged to a certain extent, 4.2V is allowed to beoutputted from the constant voltage circuit 84 to carry out constantvoltage charging (Step S301). And during this charging, the controlcircuit 87 judges whether the battery is fully charged (or nearly fullycharged) or not (Step S302). The full-charged condition is judged, forexample, by judging whether the current lowers to the charging currentcorresponding to full charge or not based on the detection data of thecurrent detection circuit 89. If it is judged that the battery is fullycharged, the output of 4.2V from the constant voltage circuit 84 isstopped by the control of the control circuit 87 and charging is stopped(step S303). It is allowed to stop charging when a specified time (forexample, 1 hour) passes from the time when the current or voltagecorresponding to full charge is detected.

And after this charging is stopped, the battery voltage of the secondarybattery 85 is detected by the voltage detection circuit 86 (Step S304).Here, it is judged whether the detected voltage value is the voltage ofstandard voltage V₁₂ or lower previously set to the control circuit 87or not (Step S305). In this example, 4.0V is used for the standardvoltage V₁₂ and for processing at Step S305, whether or not the voltageis 4.0 V or lower is judged by the control circuit 87. If it is not 4.0Vor lower, detection of the battery voltage at Step S304 is repeatedlycarried out.

For comparison processing of the voltage detected at Step S305, with4.2V outputted from the constant voltage circuit 84 set as the voltageserving as a standard, the voltage difference between this 4.2V and thebattery voltage detected by the voltage detection circuit 86 is judgedin the control circuit 87. And whether or not the voltage differenceexceeds 0.2V or not is judged to carry out processing to judge whetherthe battery voltage is 4.0V or lower.

Or for another comparison processing of the voltage at Step S305, basedon the grounding potential (that is, 0V), 4.0V may be set to the controlcircuit 87 as the standard voltage. And the battery voltage detected bythe voltage detection circuit 86 may be compared to this standardvoltage (4.0V), and processing for judging whether the battery voltageattains the standard voltage or lower may be carried out.

And when it is judged that the battery voltage is 4.0V or lower at StepS305, the timer set in the control circuit 87 is operated (Step S306).And whether a predetermined time n₁ after this timer is operated haspassed or not is judged (Step S307). For this time n₁, for example, 30minutes are assigned.

When the control circuit 87 judges the passage of time n₁ (that is,judgment that time n₁ has passed since the battery voltage reached 4.0Vor lower), processing returns to Step S301 and charging operation isstarted. For the charging operation at this time, based on the controlof the control circuit 87, 4.2V is outputted from the constant voltagecircuit 84 and constant-voltage charging is carried out using this 4.2V.And processing of Step S301 and after is repeatedly carried out.

Now referring to FIG. 31, the charging processing condition of thisexample shown in the flow chart of FIG. 30 is described. The voltagecharacteristics V₃₁ shown in FIG. 31 show changes of the batteryvoltage, carrying out charging causes the battery voltage V₃₁ approachesto a voltage V₁₁ at the full-charge, and the output of the constantvoltage circuit 84 is stopped at the timing T₁₁ when the voltage V₁₁(4.2V) is attained at the time of this full-charge, and charging to thesecondary battery 85 is stopped. By the stopping of this charging, thebattery voltage V₃₁ gradually lowers by self discharge of the battery(or discharge to the load circuit) from timing T₁₁.

Under this charging stopping condition, let detection of the batteryvoltage V₃₁ be carried out successively, and at timing T₁₂, let thebattery voltage V₃₁ lowers from the standard voltage V₂ (4.0V). In thisevent, the timer circuit in the control circuit 87 operates at timingT₁₂, and at timing T₁₃ in which time n₁ (for example, 30 minutes) passesfrom the start of the operation, charging to the secondary battery 85 isrestarted and continues to timing T₁₄ when the battery voltage V₃₁attains V₁₁ again.

By charging in this way, the timing for restarting charging is favorablyset and even if there is a detection error in the battery voltage,recharging is able to be carried out favorably, and deterioration ofbattery characteristics due to the continuation of the condition closeto the full-charge condition can be prevented. That is, when thedetection of the battery voltage V₃₁ is accurately carried out, thebattery voltage becomes a voltage sufficiently lower than the standardvoltage V₁₂ at the timing T₁₃ for restarting charging. And as shown inFIG. 31, suppose that there exists a detection error ΔVB of the batteryvoltage, and then, the timer circuit operates when the battery voltageis higher than the voltage V₁₂ by this error ΔVβ and when time n₁ passesfrom the start of the operation, such characteristics that charging isrestarted are obtained (voltage V₃₂ shown with a broken line).Consequently, even if there is a detection error of battery voltage,sufficient time is able to be secured from the restart of charging tothe return to full-charge, and deterioration of the battery due tocontinuation of the full-charge condition of the secondary battery(lithium ion battery) can be prevented.

In this event, for judgment of battery voltage detected in this example,4.2V outputted from the constant voltage circuit 84 (this 4.2V is thebattery voltage when fully charged) is designated as a standard voltage,and the voltage difference between this 4.2V and the battery voltagedetected by the voltage detection circuit 86 is judged in the controlcircuit 87 to judge the lowering of battery voltage to 4.0V or lower,and accurate judgment of the battery voltage with less error is enabled,and charging of the secondary battery is able to be controlled moresatisfactorily.

When 4.0V is designed to be judged with the voltage based on thegrounding potential (that is, 0V) without designating the batteryvoltage at the time of full-charge to the standard in this way, it ispossible for the control circuit 87 to judge the battery voltage bydirectly judging the detection data of the voltage detection circuit 86and judgment of the battery voltage can be carried out with a simpleconfiguration, but in this case, as described above, it is possible tosecure sufficient time from the restart of charging to the return to thefull charge, and deterioration of the battery caused by the continuationof the full-charged condition of the secondary battery can beeffectively prevented.

In the processing of the ninth embodiment, it is designed to carry outjudgment at the restart of charging by the detection of the batteryvoltage, but it may be designed to carry out the judgment at the restartof charging by detection of the charging current. The flow chart of FIG.32 shows charging processing in this event, which will be now describedin detail.

First of all, charging operation is carried out based on the control ofthe control circuit 87 (Step S311). In this event, with the secondarybattery 85 charged to a certain extent, 4.2V is outputted from theconstant voltage circuit 84 and constant voltage charging is carriedout. And during this charging, the control circuit 87 allows the currentdetection circuit 89 to detect the charging current (Step S312), andjudges whether the detected charging current is 100 mA or lower or not(Step S313). In this event, if the charging current exceeds 100 mA, thecontrol circuit 87 judges that the secondary battery 85 is not yet fullycharged, and allows charging at Step S311 to continue. If it judges thatthe charging current is 100 mA or lower, the control circuit judges thatthe secondary battery 85 is in the full-charge state (or nearlyfull-charged state), and the control circuit 87 changes over the outputvoltage of the constant-voltage circuit 84 to 4.0V (Step S314).

With this 4.0V constant voltage applied to the secondary battery 85, thethen charging current is detected with the current detection circuit 89(Step S315). And the control circuit 87 judges whether or not thedetected charging current is 30A or higher (Step S316). If the detectedcharging current is not 30 mA or higher, supply of 4.0V constant voltageat step 314 is carried out continuously while detection of the chargingcurrent at Step S315 is repeatedly carried out.

If the charging current is judged to be 30 mA or higher, the timercircuit in the control circuit 87 is operated (Step S317). It is judgedwhether a predetermined time n₁ has passed since this timer is operated(Step 318). For this time n₁, for example, 30 minutes may be adopted.

When the control circuit 87 judges the passage of time n₁ (that is,judgment that time n₁ has passed since the charging current attains 30mA or higher), processing returns to Step S311 and charging operation isbegun. To describe the charging operation at this time, based on thecontrol of the control circuit 87, output of the constant voltagecircuit 84 is changed over to 4.2V, and constant voltage charging iscarried out with this 4.2V. And processing after Step S311 is repeatedlycarried out.

It may be designed to stop charging when a specified time (for example,1 hour) passes after the charging current corresponding to the fullcharge is detected at Step S313.

Now, referring to FIG. 33, the charging processing condition in thisexample shown in the flow chart of FIG. 32 is described. FIG. 33 showschanges of the battery voltage V₃₁ and the charging current I, and theexecution of charging causes the battery voltage V₃₁ to approach to thevoltage V₁₁ at the time of full-charge, but as the voltage approaches tothe full-charge, the charging current I gradually decreases. At timingT₂₁ when the charging current I attains 100 mA (I₁), charging voltage V₀from the constant voltage circuit 84 is changed over to 4.0V (V₁₂). Ifthe battery voltage is 4.0V or over with this 4.0V charging voltagesupplied, the charging current scarcely flows. When the battery voltageV₃₁ lowers to 4.0V, the charging current that is detectable isgenerated, and when the charging current becomes 30 mA (I₂) or higher(timing T₂₂), the timer circuit in the control circuit 87 operates. Attiming T₂₃ when time n₁ (for example, 30 minutes) passes from the startof the operation of the timer circuit, output voltage of the constantvoltage circuit 84 is returned to 4.2V, and charging to the secondarybattery 85 by this 4.2V charging voltage is restarted, and the batteryis charged until the charging current becomes 100 mA or lower.

By charging in this way, similar to the case of detecting the voltage inthe ninth embodiment described above (at the time of processing by theflow chart of FIG. 30), timing for restarting charging is favorably set,and deterioration of characteristics of the secondary battery (lithiumion battery) caused by the continuation of the condition close to thefull-charged condition can be prevented.

Now, the 10th embodiment of this invention is described. In this 10thembodiment, charging is carried out by the charging equipment of theconfiguration shown in FIG. 29 described in the ninth embodimentdescribed above, and the charging is controlled by the control circuit87 in accordance with the flow chart of FIG. 34. The processing isdescribed hereinafter. First of all, charging operation is carried outbased on the control of the control circuit 87 (Step S321). In thisevent, with the secondary battery 85 charged to a certain extent, 4.2Vis outputted from the constant voltage circuit 84 and constant voltagecharging is carried out. And during this charging, the control circuit87 allows the current detection circuit 89 to detect the chargingcurrent (Step S322), and judges whether the detected charging current is100 mA or lower or not (Step S323). In this event, if the chargingcurrent exceeds 100 mA, the control circuit 87 judges that the secondarybattery 85 is not yet fully charged, and allows charging at Step S321 tocontinue. If it judges that the charging current is 100 mA or lower, thecontrol circuit judges that the secondary battery 85 is in thefull-charge state (or nearly full-charged state), and the controlcircuit 87 controls to stop the output voltage of the constant voltagecircuit 84 and stops charging (Step S324). It may be designed to stopcharging when a specified time (for example, 1 hour) passes after thecharging current corresponding to the full charge is detected.

At the same time as the charging is stopped, the timer circuit in thecontrol circuit 87 is operated (Step S325). It is judged whether apredetermined time n₂ (for example, 30 minutes) has passed since thistimer is operated or not (Step S326). When this time n₂ passes, thecontrol circuit 87 controls to output the 4.2V charging voltage from theconstant voltage circuit 84 and restarts charging operation temporarily(Step S327). And the charging current at this time is allowed to bedetected by the current detection circuit 89 (Step S328). And with thecontrol circuit 87, it is judged whether the charging current detectedin this event is 200 mA or higher or not (Step S329). If the chargingcurrent is not 200 mA or higher, processing returns to stop S324 to stopthe output voltage of the constant voltage circuit 84, and charging isstopped. Then, the timer circuit is started at Step S325 and every timethe time n₂ passes from the start, charging operation and detection ofthe then charging current are repeated by carried out.

When the charging current is judged to be 200 mA or higher at Step S329,processing returns to Step S321, and charging to achieve thefull-charged state is restarted.

Now, referring to FIG. 35, the charging processing condition in thisexample shown in the flow chart of FIG. 34 is described. FIG. 35 showschanges of the battery voltage V₃₁ and the charging voltage V₀, and thecharging current I, and the execution of charging causes the batteryvoltage V₃₁ to approach to the voltage V₁₁ at the time of full-charge,but as the voltage approaches to the full-charge, the charging current Igradually decreases. At timing T₃₁ when the charging current I attains100 mA (I₁), the supply of 4.2V charging voltage V₀ from the constantvoltage circuit 84 is stopped.

At the same time as this charging stops, the timer circuit in thecontrol circuit 87 operates and at timing T₃₂ when time n₂ (for example,30 minutes) passes from the start of the operation of the timer circuit,4.2V output voltage from the constant voltage circuit 84 is temporarilyrestarted. And the charging current I in this event is detected. Andwhether the charging current I is 200 mA (I3) or higher or not isjudged, but if it is 200 mA or lower, the supply of the charging voltageV₀ is stopped, and waits until the next time n₂ by the timer circuitpasses (timing T₃₃).

And while repeating detection of temporary charging current every timethis time n₂ passes, the secondary battery 85 is no longer in thefull-charged state due to self-discharge, etc., and when a specifiedcharging remainder is attained, charging current of 200 mA (I₃) orhigher is detected at 4.2V charging voltage (Timing T₃₄), and chargingof the secondary battery 85 is carried out at 4.2V constant voltage. Andat Timing T₃₅ when the charging current I becomes 100 mA (I₁) by thischarging, the battery is judged to be in the full-charged state, and thesupply of 4.2V charging voltage V₀ from the constant voltage circuit 84is stopped.

By charging in this way, after charging is stopped once the batterybecomes the full-charged state (or nearly full-charge), unless at leasta specified time n₂ (for example, 30 minutes) passes, charging is notrestarted, and moreover, charging is not restarted if the batterycharging remainder is detected to be a nearly full-charge state by thedetection of charging current every specified time n₂, and therefore,charging is not restarted unless the battery charging remainderdecreases to a certain level, thereby preventing deterioration of thecharacteristics of the secondary battery (lithium ion battery) caused bythe continuation of the nearly full-charge state.

In the processing shown in the flow chart of FIG. 34, it is designed tosupply only 4.2V, the battery voltage at the time of full-charge of thesecondary battery 85, as the output of the constant voltage circuit 84,but it may be allowed to use still lower charging voltage when temporarycharging current is detected. The flow chart of FIG. 36 shows theprocessing when the charging voltage is varied in the case of the tenthembodiment.

The processing is described hereinafter. First of all, chargingoperation is carried out based on the control of the control circuit 87(Step S331). In this event, with the secondary battery 85 charged to acertain extent, 4.2V is outputted from the constant voltage circuit 84and constant voltage charging is carried out. And during this charging,the control circuit 87 allows the current detection circuit 89 to detectthe charging current (Step S332), and judges whether the detectedcharging current is 100 mA or lower or not (Step S333). In this event,if the charging current exceeds 100 mA, the control circuit 87 judgesthat the secondary battery 85 is not yet fully charged, and allowscharging at Step S331 to continue. If it judges that the chargingcurrent is 100 mA or lower, the control circuit judges that thesecondary battery 85 is in the full-charge state (or nearly full-chargedstate), and the control circuit 87 controls to stop the output voltageof the constant voltage circuit 84 and stops charging (Step S334). Itmay be designed to stop charging when a specified time (for example, 1hour) passes after the charging current corresponding to the full chargeis detected.

At the same time as the charging is stopped, the timer circuit in thecontrol circuit 87 is operated (Step S335). It is judged whether apredetermined time n₂ (for example, 30 minutes) has passed since thistimer is operated or not (Step S336). When this time n₂ passes, thecontrol circuit 87 controls to output the 4.0V charging voltage from theconstant voltage circuit 84 and restarts charging operation temporarily(Step S337) by this 4.0V charging voltage. And the charging current atthis time is allowed to be detected by the current detection circuit 89(Step S338). And with the control circuit 87, it is judged whether thecharging current detected in this event is 30 mA or higher or not (StepS339). If the charging current is not 30 mA or higher, processingreturns to Step S334 to stop the output voltage of the constant voltagecircuit 84, and charging by the supply of the 4.0V charging voltage isstopped. Then, the timer circuit is started at Step S335 and every timethe time n₂ passes from the start, charging operation and detection ofthe then charging current are repeated.

When the charging current is judged to be 30 mA or higher at Step S339,processing returns to Step S331, 4.2V is outputted from the constantvoltage circuit 84 to carry out constant voltage charging, and chargingto achieve the full-charged state is restarted.

In this way, when the battery state is detected, by bringing thecharging voltage to 4.0V lower than 4.2V, the battery voltage at thetime of full-charge of the secondary battery 85, it is possible todetect the battery state by applying low voltage, and the battery state(charging remainder) is accurately detected with the burden to thesecondary battery reduced, and deterioration of the battery can also beprevented from this point.

Now, referring to the flow chart of FIG. 37, the case in which chargingprocessing based on the 10th embodiment is carried out by detection ofthe battery voltage will be described. First of all, when the chargingoperation begins and the battery is charged to a certain extent, 4.2V isallowed to be outputted from the constant voltage circuit 84 to carryout constant voltage charging (Step S341). And during this charging, thecontrol circuit 87 judges whether the battery is fully charged (ornearly fully charged) or not (Step S342). The full-charged condition isjudged, for example, by judging whether the current lowers to thecharging current corresponding to full charge or not based on thedetection data of the current detection circuit 89. If it is judged thatthe battery is fully charged, the output of 4.2V from the constantvoltage circuit 84 is stopped by the control of the control circuit 87and charging is stopped (Step S343). It may be allowed to stop chargingwhen a specified time (for example, 1 hour) passes from the time whenthe current or voltage corresponding to full charge is detected.

At the same time as the charging is stopped, the timer circuit in thecontrol circuit 87 is operated (Step S344). It is judged whether apredetermined time n₂ (for example, 30 minutes) has passed since thistimer is operated or not (Step S345). When this time n₂ passes, thecontrol circuit 87 controls to detect the battery voltage of thesecondary battery 85 by the voltage detection circuit 86 (Step S346).And it is judged whether the battery voltage in this event is 4.0V orlower or not (Step S347).

If the control circuit 87 judges that the battery voltage is not 4.0V orlower, it judges that the battery is still in the nearly full-chargestate, and only the energy required for detection of the battery voltageat the time is charged (Step S348). That is, 4.2V charging voltage issupplied from the constant voltage 84 circuit to the secondary battery85 only for the time previously set in the control circuit 87 (this timeis comparatively short time in proportion to the power supply consumedat the voltage detection circuit 86 at Step S346), and the battery ischarged only in accordance with how much the energy is discharged by thedetection of the battery state. Or, the battery may be charged slightlymore than that. At the same time as charging at Step S348 stops,processing returns to Step S344 to operate the timer circuit and thebattery voltage is repeatedly detected every time the time n₂ passes.

When 4.0V or lower is detected by the detection of the battery voltageat Step S357, it is judged that the secondary battery 85 has a chargingremainder of a chargeable level, and processing returns to Step S341 tooutput 4.2V from the constant voltage circuit 84, and constant voltagecharging is restarted.

Because charging processing is carried out in this way, similar to theprocessing shown in the flow chart of FIG. 34, it is possible to extendthe time before charging is restarted longer than at least the specifiedtime n₂ (for example, 30 minutes), the secondary battery chargingcondition is able to be properly maintained, and deterioration of thecharacteristics of the secondary battery can be effectively prevented.

In the processing shown in flow chart of FIG. 37, for detectionprocessing of the battery voltage at Step S346, with 4.2V outputted fromthe constant voltage circuit 84 set as the voltage serving as astandard, the voltage difference between this 4.2V and the batteryvoltage detected by the voltage detection circuit 86 is judged in thecontrol circuit 87. And whether the voltage difference exceeds 0.2V ornot is judged to carry out processing to judge whether or not thebattery voltage is 4.0V or lower.

Or, for another comparison processing of the voltage, based on thegrounding potential (that is, 0V) as a standard, 4.0V may be set to thecontrol circuit 87 as the standard voltage. And the battery voltagedetected by the voltage detection circuit 86 may be compared to thisstandard voltage (4.0V), and processing for judging whether or not thebattery voltage attains the standard voltage or lower may be carriedout.

Now the 11th embodiment of this invention will be described. In the caseof the 11th embodiment as well, charging is carried out by the chargingequipment of the configuration shown in FIG. 29 described in the 9thembodiment, and charging is controlled by the control circuit 87 inaccordance with the flow chart of FIG. 38. In the case of the 11thembodiment, the control to start recharging after waiting for thespecified time n₁ described in the 9th embodiment is combined with thecontrol to detect the battery condition every specified time n₂ afterstopping charging described in the 10th embodiment.

The processing is described hereinafter. First of all, chargingoperation is carried out based on the control of the control circuit 87(Step S351). In this event, with the secondary battery 85 charged to acertain extent, 4.2V is outputted from the constant voltage circuit 84to carry out constant voltage charging. And during this charging, thecontrol circuit 87 allows the current detection circuit 89 to detect thecharging current (Step S352), and judges whether the detected chargingcurrent is 100 mA or lower or not (Step S353). In this event, if thecharging current exceeds 100 mA, the control circuit 87 judges that thesecondary battery 85 is not yet fully charged, and allows charging atStep S351 to continue. If it judges that the charging current is 100 mAor lower, the control circuit judges that the secondary battery 85 is inthe full-charge state (or nearly full-charged state), and the controlcircuit 87 controls to stop the output voltage of the constant voltagecircuit 84 and stops charging (Step S354). It may be designed to stopcharging when a specified time (for example, 1 hour) passes after thecharging current corresponding to the full charge is detected.

At the same time as the charging is stopped, the timer circuit in thecontrol circuit 87 is operated (Step S355). It is judged whether apredetermined time n₂ (for example, 30 minutes) has passed since thistimer is operated or not (Step S356). When this time n₂ passes, thecontrol circuit 87 controls to output the 4.2V charging voltage from theconstant voltage circuit 84 and restarts charging operation temporarily(Step S357). And then charging current is allowed to be detected by thecurrent detection circuit 89 (Step S358). And with the control circuit87, it is judged whether the charging current detected in this event is200 mA or higher or not (Step S359). If the charging current is not 200mA or higher, processing returns to Step S354 to stop the output voltageof the constant voltage circuit 84, and charging is stopped. Then, thetimer circuit at Step S355 is started and every time the time n₂ passesfrom the start, charging operation and detection of the then chargingcurrent are repeated by carried out.

When the charging current is judged to be 200 mA or higher at Step S359,the timer circuit in the control circuit 87 is operated again (StepS360). And judgment is made on whether the predetermined time n₁ haspassed or not after the timer is operated at this Step S360. For thistime n₁, for example, 30 minutes are designated.

When the control circuit 87 judges the passage of time n₁ (that is,judgment that time n₁ has passed since the charging current attains 200mA or higher), processing returns to Step S351 to start chargingoperation. For the charging operation in this event, based on thecontrol of the control circuit 87, the output of the constant voltagecircuit 84 is changed over to 4.2V to carry out constant voltagecharging by this 4.2V. And processing after Step S351 on is repeatedlycarried out.

Because charging processing is carried out in this way, the detectionprocessing of this secondary battery state after charging to thesecondary battery is stopped is carried out every time the time n₂passes by the timer circuit, and control for properly maintain thesecondary battery charging state is favorably carried out, and at thesame time, because when it is judged by the detection every time n₂ thatthe battery charging remainder is in the chargeable condition,recharging is designed to be started after waiting time n₁ passes bymeans of the timer circuit, the period before the secondary batteryreturns to the full-charged state is able to be constantlysatisfactorily maintained irrespective of then detection accuracy, andfrom this point, as well, control for properly maintaining the secondarybattery charging condition is carried out.

In this 11th embodiment, the charging voltage at the time of temporarycharging after charging stops is designed to be 4.2V, same as that atthe time of regular charging, but the charging voltage at the time oftemporary charging may be designated to low voltages, such a 4.0V or thelike. By doing so, it is possible to reduce burdens applied to thesecondary battery when the battery condition is detected.

In place of detecting the secondary battery condition by the currentvalue, it may be allowed to detect the secondary battery condition withthe battery voltage. In the case of detecting this battery voltage, whenthe battery voltage is detected under the charging stopping state, theenergy discharged from the secondary battery for the detection may becharged.

Now, referring to FIG. 39 to FIG. 41, the 12th embodiment of thisinvention will be described.

FIG. 39 is a block diagram showing the configuration of the chargingequipment of this example, where AC power supply is supplied from acommercial AC power supply 101 to a rectifier circuit 102 comprising adiode bridge to provide DC power supply. And this DC power supply issupplied to a primary side control circuit 103, and at the primary sidecontrol circuit 103. A specified processing is carried out in theprimary side control circuit 103 and then supplied to a primary sidewinding 104a of a switching transformer 104. And at a secondary sidewiring 104b of the switching transformer 104, DC low-voltage powersupply converted to a specified low voltage is obtained. To theprimary-side control circuit 103, a control signal is supplied from avoltage detection circuit 111 or 112 on the secondary side laterdescribed via a photocoupler 113, and the output voltage is controlledin accord with this control signal. This primary side control circuit isconfigured with integrated circuits.

One end of the secondary winding 104b of this switching transformer 104is connected to the anode of a switching diode 105, and the cathode ofthis diode 105 and the other end of the secondary winding 104b areconnected by a switching capacitor 106 to provide a DC low-voltage powersupply of a specified voltage.

The anode of the diode 105 from which the low-voltage DC power supply isobtained is connected to one end of a connecting switch SW11 and theother end of the connecting switch SW11 in connected to one end(positive electrode) of a secondary battery 107 (here, lithium ionbattery is used for the secondary battery) loaded on this chargingequipment. The connecting switch SW11 is controlled to turn on and offby a later-described charging control circuit 109, and comprised of aswitch such as a relay or the like in addition to a semiconductor switchsuch as a field effect transistor (FET) or the like. However, when thesemiconductor switch is used, it is preferable to use the field effecttransistor with less loss at the time of conduction.

And the other end (negative electrode) of the secondary battery 107 isconnected to the other end of the secondary winding 104b of theswitching transformer 104. Across the other end (negative electrode) ofthis secondary battery 107 and the other end of the secondary winding104b of the switching transformer 104, a charging control means such asthe field-effect transistor, etc. may be connected.

Across one end and the other end of the secondary battery 107, a voltagedetection circuit 108 is connected for detecting the battery voltage,and the detection output of this voltage detection circuit 108 issupplied to the charging control circuit 109. At the charging controlcircuit 109, based on the detection condition of the battery voltage,ON/OFF control is carried out on the connecting switch SW11. Thecharging control circuit 109 comprises integrated circuits, whosecontrol condition will be later discussed based on the flow chart ofFIG. 40.

On the cathode side of the diode 105, two voltage detection circuits areconnected. That is, the 4.2V detection circuit 111 and the 4.1Vdetection circuit 112 are connected, and at each of the detectioncircuits 111, 112, voltage detection with 4.2V or 4.1V set as a standardis carried out, and the detection error information (that is,information on the difference between voltage values used for thestandard) is obtained, and of the detection error informations of bothdetection circuits 111, 112, the information selected by a change-overswitch SW12 is supplied to the primary side control circuit 103 as aswitching control signal via the photocoupler 113. Consequently, if thechangeover switch SW12 is set to the 4.2V detection circuit 111 side,the power supply of the 4.2V voltage is controlled to be obtained on thecathode side of the diode 105, and when the changeover switch SW12 isset to the 4.1V detection circuit 112 side, the power supply of 4.1Vvoltage is controlled to be obtained on the cathode side of the diode105. The change-over of the changeover switch SW12 is controlled by thecharging control circuit 109.

The charging equipment of this example is configured as described above,but there is a case in which some load circuit 110 may be connected tothe secondary battery 107.

Now, referring to the flow chart of FIG. 40, operation when thesecondary battery 107 is charged with the charging equipment of theconfiguration of FIG. 39 is described. In the case of this example, alithium ion battery with the 4.2V battery voltage at the time offull-charge is used for the secondary battery 107.

If the charging remainder of the secondary battery 107, the lithium ionbattery, is lower than a specified level, the charging control circuit109 controls to turn on the connecting switch SW11 with the connectingswitch SW12 set to the 4.2V detection circuit 111 side, and supply 4.2Vto the secondary battery 107 for charging (Step S401). It is determinedwhether or not the battery is charged to the full-charge (or a specifiedcapacity close to the full-charge) by detection of the battery voltageor the like (Step S402), and if it is determined that the battery isfully charged, then the control circuit turns off the connecting switchSW11 to stop charging (Step 403). And the control circuit allows theconnecting switch SW12 to change over to the 4.1V detection circuit 112side (Step S404).

Under this condition, the charging control circuit 109 judges a batteryvoltage detected by the battery voltage detection circuit 108 (StepS405). It is determined whether or not the battery voltage is lower than4.1V (Step S406). If it is determined that the battery voltage is notlower than 4.1V, then the decision processing of the battery voltage instep S405 is continued. If it is determined that the battery voltage islower than 4.1V, then, after waiting for a predetermined time (forexample, several minutes to several tens of minute) to pass (Step S407),it is again determined whether the battery voltage is lower than 4.1V(Step S408). If it is determined that the battery voltage is not lowerthan 4.1V, then the processing returns to the decision processing forthe battery voltage in step S405. If it is determined in thebattery-voltage judgement processing in Step S408 again that the batteryvoltage is lower than 4.1V, then the connection switch SW11 is turned on(Step S409). Since the connecting switch SW12 is set to the 4.1Vdetection circuit 112 side at this time, the secondary battery ischarged until the battery voltage becomes 4.1V. Thereafter, a so-calledtrickle charging is carried out in which detection as to whether or notthe battery voltage is lower than 4.1V and the restart of chargingoperation after a predetermined time since the detection are repeatedlycarried out.

Because after the secondary battery is once charged to full-charge (ornearly full-charged condition) by charging as shown in the flow chart ofFIG. 40, the switch SW11 between the charging circuit side and thesecondary battery is turned off, and only when the battery voltage isdetected under this condition and the conditions up to Step S408 aresatisfied, the switch SW11 is turned on and charging is resumed, underthe condition where charging is stopped, the charging circuit and thesecondary battery are held separated, preventing wasteful discharge fromthe battery because the voltage set on the charging circuit side (4.1V)is lower than the battery voltage (4.2V). In addition, because for acondition to resume charging at 4.1V, charging is designed to be resumedonly when passage of a specified time is waited at Step S407 after thebattery voltage 4.1V or lower is detected, and the battery voltage 4.1Vor lower is detected in such event, it is the condition in which thebattery voltage is accurately lower than 4.1V (because self-discharge ordischarge to the load circuit takes place after 4.1V or lower is firstdetected), and the trickle charge at 4.1V is accurately carried out.

As described in the flow chart of FIG. 40, in stead of waiting thepassage of a specified time at Step S407 after detecting the batteryvoltage of 4.1V or lower, it may be designed to detect a specifiedvoltage lower than 4.1V (for example, 4.0V). That is, for example, asshown in the flow chart of FIG. 41, by carrying out battery voltagedetection processing at Step S405 (same as processing of FIG. 40 up toStep S405), whether the battery voltage is 4.0V or lower or not isjudged (Step S411). If it is judged to be 4.0V or lower at this step,the connection switch SW11 is brought to the ON state (Step S412), andthe secondary battery 107 is charged at 4.1V. And thereafter, detectionof battery voltage of 4.0V or lower and resumption of charging at 4.1Vare repeatedly carried out, achieving so-called trickle charging.

Carrying out charging by the processing shown in FIG. 41 eliminates aneed for counting the passage of a required time at the charging controlcircuit, and simplifies the configuration for charging control as much.

Next referring to FIG. 42 and FIG. 43, the 13th embodiment of thepresent invention is described. In FIG. 42 showing the configuration ofthe charging equipment according to this 13th embodiment, partscorresponding to those in FIG. 39 which shows a configuration of the12th embodiment are denoted by the same reference numerals, and theirdetailed description is omitted.

In this example as well, the charging equipment is designed to chargethe secondary battery 107, a lithium ion battery, and in this case, inplace of providing a circuit for detecting the battery voltage, apotential difference detection circuit 121 for detecting the potentialdifference between one end and the other of the connecting switch SW11is provided, and based on the detection data of this detection circuit121, a charging control circuit 122 is designed to carry out ON/OFFcontrol of the switch SW11.

That is, the potential difference detection circuit 121 detects not onlythe potential E₀ across one end of the connecting switch SW11 (sideconnected to the diode 105) and the negative electrode side of thesecondary battery 107 (that is, the other end of the secondary winding104b of the switching transformer) but also the potential E_(B) acrossthe other end of the connecting switch SW11 (the side connected to thesecondary battery 107) and the negative electrode side of the secondarybattery 107. And the relationship of the magnitude between the detectedpotential E₀ and the potential E_(B) is judged and the judgment resultsare supplied to the charging control circuit 122. In the chargingcontrol circuit 122, based on the results, switches SW11 and SW12 arecontrolled to control the charging. This charging control circuit 122comprises integrated circuits, and the control condition thereof will belater described based on the flow chart of FIG. 43. Other parts areconfigured in the same manner as in the case of the charging equipmentshown in FIG. 39.

Now referring to the flow chart of FIG. 43, operation when the secondarybattery 107 is charged with the charging equipment of the configurationof FIG. 42 is described. In the case of this example, a lithium ionbattery with the 4.2V battery voltage at the time of full-charge is usedfor the secondary battery 107.

If the charging remainder of the secondary battery 107, the lithium ionbattery, is lower than a specified volume, the charging control circuit122 controls to turn on the connecting switch SW11 with the connectingswitch SW12 set to the 4.2V detection circuit 111 side, and supply 4.2Vto the secondary battery 107 for charging (Step S431). It judges whetheror not the battery is charged to the full-charge (or a specifiedcapacity close to the full-charge) by detection of the battery voltage,etc., and if it judges that the battery is fully charged, the controlcircuit turns off the connecting switch SW11 to stop charging (Step433). And the control circuit allows the connecting switch SW12 tochange over to the 4.1V detection circuit 112 side (Step S434).

Under this condition, the potential E₀ and the potential E_(B) aredetected by the potential difference detection circuit 121 (Step S435),and it is judged whether or not the power supply voltage E₀ is higherthan the battery voltage E_(B) (Step S436). In this event, if the powersupply voltage E₀ is judged to be higher, after waiting for apredetermined time (for example, a few minutes to scores of minutes) topass (Step S437), it is again judged whether or not the power supplyvoltage E₀ is higher than the battery voltage E_(B) (Step S438). If thebattery voltage E_(B) is higher than the power supply voltage E₀,processing returns to the potential difference judgment at Step S436.And if in the repeated potential difference judgment at Step S438. Thepower supply voltage E₀ is judged to be higher, the connection switchSW11 is turned on (Step S439). In this event, because the connectingswitch SW12 is set to the 4.1V detection circuit 112 side, the secondarybattery 107 is charged with 4.1V.

Because after the secondary battery is once charged to full-charge (ornearly full-charged condition) by charging as shown in the flow chart ofFIG. 43, similar to the case of the 12th embodiment described above, theswitch SW11 between the charging circuit side and the secondary batteryis turned off, and only when the battery voltage is detected under thiscondition and the conditions up to Step S438 are satisfied, the switchSW11 is turned on and charging is resumed, under the condition wherecharging is stopped, the charging circuit and the secondary battery areheld separated, preventing wasteful discharge from the battery becausethe voltage set on the charging circuit side (4.1V) is lower than thebattery voltage (4.2V). In addition, because charging is designed to beresumed only when passage of a specified time is waited at Step S437after the battery voltage is detected to be lower than the power supplyvoltage (that is, 4.1V or lower), and the battery voltage is detected tobe lower than the power supply voltage in such event, charging isdefinitely resumed under the condition in which the battery voltage islower than the power supply voltage.

In the 13th embodiment, the battery voltage is judged by the comparisonwith the power supply voltage, it is possible to correctly judge thebattery voltage, and judgment for resuming charging can be accuratelycarried out.

Now referring to FIG. 44 and FIG. 45, the 14th embodiment of the presentinvention is described. In FIG. 44 showing the configuration of thecharging equipment according to this 14th embodiment, partscorresponding to those in FIG. 39 which shows the configuration of the12th embodiment are denoted by the same reference numerals, and theirdetailed description is omitted.

In this example as well, the charging equipment is designed to chargethe secondary battery 107, a lithium ion battery, and in this case, inaddition to a battery voltage detecting circuit 108, a resistor 132 fordetecting the current flowing through the secondary battery 107 isconnected to the secondary battery 107 in series, and the potentialacross both ends of this resistor 132 is detected with a detectioncircuit 133, and the current flowing through the secondary battery 107is designed to detect with a detection circuit 133. And the data of thecurrent value detected by this detection circuit 133 are supplied to acharging control circuit 131. The data on battery voltage detected bythe battery voltage detection circuit 108 is supplied to the chargingcontrol circuit 131.

In the charging control circuit 131, based on each detection datasupplied, the connecting switch SW11 is controlled to turned on and off,and at the same time, the change-over of the connecting switch SW12 isalso controlled. This charging control circuit comprises integratedcircuits, and the control condition thereof will be later describedbased on the flow chart of FIG. 45. Other parts are configured in thesame manner as in the case of the charging equipment shown in FIG. 39.

Now, referring to the flow chart of FIG. 45, operation when thesecondary battery 107 is charged with the charging equipment of theconfiguration of FIG. 44 is described. In the case of this example, alithium ion battery with the 4.2V battery voltage at the time offull-charge is used for the secondary battery 107.

If the charging remainder of the secondary battery 107, the lithium ionbattery, is lower than a specified amount, the charging control circuit131 controls to turn on the connecting switch SW11 with the connectingswitch SW12 set to the 4.2V detection circuit 111 side, and supply 4.2Vto the secondary battery 107 for charging (Step S441). It judges whetheror not the battery is charged to the full-charge (or a specifiedcapacity close to the full-charge) by detection of the battery voltage,etc. (Step S442), and if it judges that the battery is fully charged,the control circuit turns off the connecting switch SW11 to stopcharging (Step S443). And the control circuit allows the connectingswitch SW12 to change over to the 4.1V detection circuit 112 side (StepS444).

Under this condition, the current flowing the secondary battery 107detected by the current detection circuit 133 is judged by the chargecontrol circuit 131 (Step S445). In this event, it is judged whether ornot the current value is a predetermined threshold value Ix A or lower(Step S446). This threshold value Ix A is set in advance based on thebattery characteristics. In this event, if it is lower than Ix A, it isjudged that there is discharge to the load circuit 110, and currentdetection at Step S445 is repeatedly carried out. And if the currentdetected at Step S446 is judged to be lower than Ix A, battery voltageis judged based on the detection data of the battery voltage detectioncircuit 108 (Step S447). And in this event, the battery voltage isjudged to be 4.1V or lower (Step S448) or not, and it is judged to be4.1V or lower, the connecting switch SW11 is turned on (Step S449), andcharging at 4.1V is resumed. For judgment of this battery voltage, as inthe case of the processing described in the 12th embodiment (processingat Step S407, S408 in the flow chart of FIG. 40), charging may beresumed after a specified time passes if 4.1V or lower is againdetected.

Because after the secondary battery is once charged to full-charge (ornearly full-charged condition) by charging as shown in the flow chart ofFIG. 45 similar to the case of the first embodiment described above, theswitch Sw11 between the charging circuit side and the secondary batteryis turned off, and only when the battery voltage is detected under thiscondition and the conditions up to Step S448 are satisfied, the switchSW11 is turned on and charging is resumed, under the condition wherecharging is stopped, the charging circuit and the secondary battery areheld separated, preventing wasteful discharge from the battery becausethe voltage set on the charging circuit side (4.1V) is lower than thebattery voltage (4.2V).

And in the 14th embodiment, because the battery voltage is judged andtrickle charge at 4.1V is designed to be carried out after confirmingthat there is no discharge exceeding a specified volume from the battery107 to the load circuit 110 side, if there is any discharge exceeding aspecified volume from the battery 107 to the load circuit 110 side,trickle charge treatment in this example is not carried out, and tricklecharge is properly carried out only when it is required. When thecharging remainder of the battery is considerably reduced due to thedischarge to the load circuit 110, regular charging at 4.2V (that is,charging treatment conventionally known) is carried out by anothercontrol system not illustrated.

Now referring to FIG. 46 and FIG. 47, the 15th embodiment of the presentinvention is described. In FIG. 46 showing the configuration of thecharging equipment according to this 15th embodiment, partscorresponding to those in FIG. 39, FIG. 42, and FIG. 44 which showconfigurations of the 12th, 13th, and 14 embodiments, respectively, aredenoted by the same reference numerals, and their detailed descriptionis omitted.

In this example as well, the charging equipment is designed to chargethe secondary battery 107, a lithium ion battery, and in this case, theresistor 132 for detecting the current flowing through the secondarybattery 107 is connected in series to the secondary battery 107, and thepotential across both ends of this resistor 132 is detected with thedetection circuit 133 and the current flowing through the secondarybattery 107 is designed to detect with the detection circuit 133. Inaddition, a potential difference detection circuit 121 for detecting thepotential difference between one end and the other of the connectingswitch Sw11 is provided, and with this potential difference detectioncircuit 121, the power supply potential E₀ and the battery potentialE_(B) are detected, and the relationship of the magnitudes between thedetected power supply potential E₀ and the battery potential E_(B) isjudged and the judgment results are supplied to a charging controlcircuit 141. In the charging control circuit 141, based on the currentdetection data from the detection circuit 133 and the potentialdifference detection data from the detection circuit 121, the switchesSW11 and SW12 are controlled to control the charging. This chargingcontrol circuit 141 comprises integrated circuits, and the controlcondition thereof will be later described based on the flow chart ofFIG. 47. Other parts are configured in the same manner as in the case ofthe charging equipment shown in FIG. 39.

Now referring to the flow chart of FIG. 47, operation when the secondarybattery 107 is charged with the charging equipment of the configurationof FIG. 46 is described. In the case of this example, a lithium ionbattery with the 4.2V battery voltage at the time of full-charge is usedfor the secondary battery 107.

If the charging remainder of the secondary battery 107, the lithium ionbattery, is lower than a specified volume, the charging control circuit141 controls to turn on the connecting switch SW11 with the connectingswitch SW12 set to the 4.2V detection circuit 111 side, and supply 4.2Vto the secondary battery 107 for charging (Step S451). It judges whetheror not the battery is charged to the full-charge (or a specifiedcapacity close to the full-charge) by detection of the battery voltage,etc. (Step S452), and if it judges that the battery is fully charged,the control circuit turns off the connecting switch SW11 to stopcharging (Step S453). And the control circuit allows the connectingswitch SW12 to change over to the 4.1V detection circuit 112 side (StepS454).

Under this condition, the current flowing through the secondary battery107 detected by the current detection circuit 133 is judged by thecharging control circuit 141 (step S455). In this event, it is judgedwhether or not the current value is the predetermined threshold value IxA or lower (Step S456). In this event, if it is not lower than Ix A, itis judged that there is discharge to the load circuit 110, and thecurrent detection at Step S455 is repeatedly carried out. And if thecurrent value detected at Step S456 is judged to be lower than Ix A,potential E₀ and potential E_(B) are detected by the potentialdifference detection circuit 121 (Step S457) and it is judged whetherthe power supply voltage E₀ is higher than the battery voltage E_(B)(Step S458) or not. If it is judged that the power supply voltage E₀ ishigher, the connection switch SW11 is turned on (Step S459) to resumetrickle charging at 4.1V. If the battery voltage E_(B) is higher thanthe power supply voltage E₀, processing returns to the potentialdifference judgment at Step S457. For judgment of this potentialdifference, as with the processing described in the 13th embodiment(processing at Steps S437, S438 of the flow chart of FIG. 43), chargingmay be designed to be resumed when the power supply voltage E₀ is againdetected to be higher after a specified time passes.

Because after the secondary battery is once charged to full-charge (ornearly full-charged condition) by charging as shown in the flow chart ofFIG. 47, as in the case of each embodiment described above, the switchSW11 between the charging circuit side and the secondary battery isturned off, and only when the battery voltage is detected under thiscondition and the conditions up to Step S458 are satisfied, the switchSW11 is turned on and charging is resumed, under the condition wherecharging is stopped, the charging circuit and the secondary battery areheld separated, preventing wasteful discharge from the battery becausethe voltage set on the charging circuit side (4.1V) is lower than thebattery voltage (4.2V). In this event, since the battery voltage isjudged by the comparison of the power supply voltage, the batteryvoltage is able to be accurately judged and the judgment of resumingcharging is able to be accurately made.

In the 15th embodiment, because after making sure there is no dischargeexceeding a specified volume from the battery 107 to the load circuit110 side, the battery voltage is judged and trickle charging by 4.1V isdesigned to be carried out, if any discharge exceeding the specifiedvolume exists from the battery 107 to the load circuit 110 side, tricklecharge processing of this example is not carried out, but is properlycarried out only when trickle charge is needed. When the chargingremainder of the battery is considerably reduced due to the discharge tothe load circuit 110, regular charging at 4.2V (that is, chargingtreatment conventionally known) is carried out by another control systemnot illustrated.

Now, referring to FIG. 48 and FIG. 49, the 16th embodiment of thisinvention will be described. In FIG. 48 showing the configuration of thecharging equipment according to this 16th embodiment, partscorresponding to those in FIG. 39 which shows configuration of the 12thembodiment, are denoted by the same reference numerals, and theirdetailed description is omitted.

In this example as well, the charging equipment is designed to chargethe secondary battery 107, a lithium ion battery, and in this case, inparallel with the connecting switch SW11 for controlling the supply ofcharging voltage to the secondary battery 107, a charging current supplypath and a current detection means of the supply path are connected.That is, one end of the connecting switch SW11 (the side connected tothe diode 105) is connected to the emitter of a PNP type transistor 152,and the collector of this transistor 152 is connected to the other end(side connected to the secondary battery 107) of the connecting switchSW11 via a resistor 151. And the base of the transistor 152 is connectedto the other end of the secondary winding 104b of the switchingtransformer via a resistor 153, and the emitter and the base of thetransistor 152 are the connected by a resistor 154. And the potentialacross both ends of this resistor 151 is detected with a detectioncircuit 155 and based on the potential detection thereof, the chargingcurrent supplied from the diode 105 side to the secondary battery 107 isdetected. This charging current detection data is supplied to a chargingcontrol circuit 156. In the charging control circuit 156, based on thecurrent detection data from the detection circuit 155, switches SW11 andSW12 are controlled to control the charging. This charging controlcircuit 156 comprises integrated circuits, and the control conditionthereof will be later described based on the flow chart of FIG. 49. Byconnecting the transistor 152 to its surrounding circuits as shown inFIG. 49, the current flow via this transistor 152 becomes only the flowfrom the diode 105 side to the secondary battery 107 side, and nocurrent in the reverse direction is generated. Other parts areconfigured in the same manner as in the case of the charging equipmentshown in FIG. 39.

Now referring to the flow chart of FIG. 49, operation when the secondarybattery 107 is charged with the charging equipment of the configurationof FIG. 48 is described. In the case of this example, a lithium ionbattery with the 4.2V battery voltage at the time of full-charge is usedfor the secondary battery 107.

If the charging remainder of the secondary battery 107, the lithium ionbattery, is lower than a specified volume, the charging control circuit156 controls to turn on the connecting switch SW11 with the connectingswitch SW12 set to the 4.2V detection circuit 111 side, and supply 4.2Vto the secondary battery 107 for charging (Step S461). It judges whetheror not the battery is charged to the full-charge (or a specifiedcapacity close to the full-charge) by detection of the battery voltage,etc. (Step S462), and if it judges that the battery is fully charged,the control circuit turns off the connecting switch Sw11 to stopcharging (Step S463). And the control circuit allows the connectingswitch SW12 to change over to the 4.1V detection circuit 112 side (StepS464).

Under this condition, the current flowing through the secondary battery107 detected by the current detection circuit 155 is judged by thecharging control circuit 156 (Step S465). In this event, it is judgedwhether the current value is a predetermined threshold value Ix A orhigher (Step S466). In this event, if it is not lower than Ix A, it isjudged that charging current exceeding a specified volume is notgenerated, and current detection at Step S465 is repeatedly carried out.And if the current detected at Step S466 is judged to be higher than IxA (that is, the condition in which the charging volume of the secondarybattery 107 decreases and charging current is supplied to some extent),after waiting for a predetermined time (for example, a few minutes toscores of minutes) to pass (Step S467), it is again judged whether thecurrent is the predetermined threshold value Ix A or higher (Step S468).In this event, if it is judged not to be higher than Ix A, processingreturns to the current judgment at Step S465. And by the repeatedcurrent judgment at Step S468, if it is judged that the current ishigher than the threshold value Ix A, the connecting switch SW11 isturned on (Step S469). In this event, because the connecting switch SW12is set to the 4.1V detection circuit 112 side, the secondary battery 107is charged at 4.1V. Thereafter, detection of the charging current andresumption of charging after a specified time passes after the detectionare repeated carried out, and the so-called trickle charging is carriedout.

Because the secondary battery is charged as shown in the flow chart ofFIG. 49, trickle charging is favorably controlled based on the detectionof the charging current. In this case, too, it is possible to preventwasteful discharge from the secondary battery 107 with charging stoppedto the charging circuit side, and in addition, because it is designed tojudge that the current higher than the specified current continues toflow for a specified time and to resume charging after detecting thecurrent higher than the specified value when charging is resumed, thebattery is accurately checked for the condition suited for resumingcharging; thereby proper charging processing can take place. That is,when constant voltage is applied, the lithium ion battery has suchcharacteristics which tend to increase charging current as the batterycharging remainder decreases, and making the best use of thecharacteristics, resumption of charging can be accurately judged.

Now, referring to FIG. 50, the 17th embodiment of this invention will bedescribed. In FIG. 50 showing the configuration of the chargingequipment according to this 17th embodiment, parts corresponding tothose in FIG. 39 which shows the configuration of the 12th embodiment,are denoted by the same reference numerals, and their detaileddescription is omitted.

In this example as well, the charging equipment is designed to chargethe secondary battery 107, a lithium ion battery, and in this case, aswith the case of the 16th embodiment, in parallel with the connectingswitch SW11 for controlling the application of charging voltage to thesecondary battery 107, a current detection means is provided, but in thecase of this example, this current detection means is designed to beconnected to a power supply different from the system to which theswitch SW11 is connected.

That is, to the switching transformer 104, an auxiliary winding 104c isprovided separately from the secondary winding 104b, and to one end ofthis auxiliary winding 104c, the anode of a switching diode 161 isconnected, and the cathode of this diode 161 and the other end of theauxiliary winding 104c are connected by a switching capacitor 162. Andthe other end of the auxiliary winding 104c and the other end of thesecondary winding 104b are connected in common.

And the cathode of the diode 161 is connected to the collector of a NPNtype transistor 163, and the other end of the auxiliary winding 104c isconnected to the base of the transistor 163 via a zener diode 164. Andthe collector and the base of this transistor 163 are connected with aresistor 165. And the emitter of the transistor 163 is connected to oneend (positive electrode) of the secondary battery 107 via a resistor 166for current detection.

And the voltage across both ends of this resistor 166 is detected with adetection circuit 167 and current flowing through the resistor 166 isdetected. This current detection data is supplied to a charging controlcircuit 168 and based on the current detection data from the detectioncircuit 167, switches SW11 and SW12 are controlled to control thecharging. Other parts are configured in the same manner as in the caseof the charging equipment shown in FIG. 39.

By configuring in this way, as with the case of the 26th embodimentdescribed above, it is possible to judge the resumption of charging fromthe charging current, thereby achieving favorable charging control. Forcharging control with the charge control circuit 168, for example,processing of the flow chart of FIG. 49 described in the 16th embodimentis recommended to carry out.

Now, referring to FIG. 51 and FIG. 52, the 18th embodiment of thisinvention will be described. In FIG. 51 showing the configuration of thecharging equipment according to this 18th embodiment, partscorresponding to those in FIG. 39 which shows the configuration of the12th embodiment, are denoted by the same reference numerals, and theirdetailed description is omitted.

In this example as well, the charging equipment is designed to chargethe secondary battery 107, a lithium ion battery, and in this case, inparallel with the connecting switch SW11, a series circuit comprising aconnecting switch SW13 and a constant current circuit 171 is connected.And based on the detection data of the battery voltage detection circuit108 of the secondary battery 107, a charging control circuit 172 isdesigned to control connecting switches SW11, SW13, and changeoverswitch SW12. For the output current of the constant current circuit 171,for example, comparatively small current suited for trickle charging isused. Other parts are configured in the same manner as in the case ofthe charging equipment shown in FIG. 39.

Now referring to the flow chart of FIG. 52, operation when the secondarybattery 107 is charged with the charging equipment of the configurationof FIG. 51 is described. In the case of this example, a lithium ionbattery with the 4.2V battery voltage at the time of full-charge is usedfor the secondary battery 107.

First of all, if the charging remainder of the secondary battery 107,the lithium ion battery, is lower than a specified volume, the chargingcontrol circuit 172 controls to supply 4.2V to the secondary battery forcharging (Step S471) with the changeover switch SW12 set to the 4.2Vdetection circuit 111 side and the connecting switch SW11 turned on(connecting switch SW13 is held turned off). It is judged whether thebattery is charged to the full-charge (or a specified capacity close tothe full-charge) by detection of the battery voltage, etc. (Step S472),and if it is judged that the battery is fully charged, the controlcircuit turns off the connecting switch SW11 (the connecting switch SW13is held turned off) to stop charging (Step S473). And the controlcircuit allows the changeover switch SW12 to change over to the 4.1Vdetection circuit 112 side (Step S474).

Under this condition, the battery voltage detected by the currentdetection circuit 108 is judged by the charging control circuit 172(Step S475), In this event, it is judged whether or not the batteryvoltage is 4.1V or lower (Step S476). In this event, if it is not lowerthan 4.1V, judgment of the battery voltage at Step S475 is continuouslycarried out. If it is determined that the battery voltage is lower than4.1V, then, after waiting for predetermined time (for example, severalminutes to several tens of minute) to pass (Step S477), it is againdetermined whether or not the battery voltage is lower than 4.1V (StepS478). If it is determined that the battery voltage is not lower than4.1V, then the processing returns to the decision processing for thebattery voltage is step S475. If it is determined in the battery-voltageis lower than 4.1V, then the connection switch SW13 is turned on (StepS479). In this event, the connection switch SW11 is kept in itsoff-state.

In this event, because the changeover switch SW12 is set to the 4.1Vdetection circuit 112 side, the constant current output by the constantcurrent circuit 171 at 4.1V voltage is supplied to charge the secondarybattery 107 until the battery voltage achieves 4.1V. Thereafter,detection of the charging current and resumption of charging after aspecified time passes after the detection are repeated carried out, andso-called trickle charging is carried out.

Because the secondary battery is charged as shown in the flow chart ofFIG. 52, after the secondary battery is charged once to the full-charge(or, the condition close to full-charge), the switch SW11 across thecharging circuit side and the secondary battery is turned off, it ispossible to prevent wasteful discharge as with the case of the 11thembodiment. And only when the battery voltage is detected under thisstate and conditions up to Step S478 are satisfied, constant currentcharging with switch SW13 turned on is carried out, and charging byconstant current can be carried out. Because charging by the constantcurrent is carried out in this way, even when the secondary battery 107or load circuit 110 is shorted due to a certain factor, only thecharging current restricted by the constant current circuit 171 issupplied to the battery side, and hence there is no case in which largecurrent flows to the battery side.

Charging processing in the 18th embodiment is described using an examplewith the constant current circuit and switch SW13 connected to thecharging equipment of the 12th embodiment, but this may be achieved byconnecting the series circuit of the constant current output circuit andswitch SW13 in parallel to the connecting switch SW11 of the chargingequipment from the 13th embodiment to the 17th embodiment describedabove. For the control of this case, only when trickle charging isresumed, the connecting switch SW13 is turned on, and when other uponother charging, the connecting switch SW11 is turned on.

In each of the above-mentioned embodiments, description is made on thecases when a lithium ion battery is charged as the secondary battery,but needless to say that it can be applied to the charging equipment ofthe secondary battery requiring charging at other similarcharacteristics. Values of voltage, current to be charged to full-chargeor the like, and time to be set at the timer circuit or the like may beappropriately selected in accord with the voltage characteristics, etc.of the battery used, and shall not be restricted to the values of eachof the above-mentioned embodiments.

    ______________________________________                                        EXPLANATION OF REFERENCE NUMBERS                                              ______________________________________                                        1            the switching transformer                                        2            the diode                                                        3            the capacitor                                                    4            the secondary battery                                            5            the resistor                                                     6            the control circuit                                              7            the control circuit                                              11           the commercial AC power supply'                                  12           the transformer/rectifier circuit                                13           the constant current circuit                                     14           the changeover switch                                            14a          the first fixed contact                                          14b          the second fixed contact                                         14m          the movable contact                                              15           the constant voltage circuit (for outputting                                  4.2 V)                                                           16           the constant voltage circuit (for outputting                                  4.0 V)                                                           17           the secondary battery (lithium ion battery)                      18           the voltage detection circuit                                    19           the current detection resistor                                   20           the current detection circuit                                    21           the control circuit                                              22           the changeover switch                                            22a          the first fixed contact                                          22b          the second fixed contact                                         22c          the third fixed contact                                          22m          the movable contact                                              23           the constant voltage circuit (for outputting                                  4.2 V)                                                           24           the constant voltage circuit (for outputting                                  4.1 V)                                                           25           the constant voltage circuit (for outputting                                  4.0 V)                                                           26           the control circuit                                              27           the temperature sensor                                           28           the load circuit                                                 41           the commercial AC power supply                                   42           the rectifier circuit                                            43           the primary-side control circuit                                 44           the switching transformer                                        44a          the primary-side winding                                         44b          the secondary-side winding                                       44c          the auxiliary winding                                            45           the diode                                                        46           the capacitor                                                    47           the secondary battery (lithium ion battery)                      48           the field effect transistor                                      49           the parasitic diode                                              50           the charging control circuit                                     51           the voltage detection circuit                                    52           the photocoupler                                                 52a          the light emitting diode                                         52b          the photosensor                                                  53           the voltage detection circuit                                    54           the charging control circuit                                     55           the voltage detection/charging control circuit                   56, 56       the resistors                                                    58           the transistor                                                   59           the Zener diode                                                  60           the resistors                                                    62           the transistor                                                   63           the resistor                                                     64, 65, 66   the Zener diodes                                                 67           the changeover switch                                            71           the first constant voltage source                                72           the second constant voltage source                               73           the changeover switch                                            74           the diode                                                        75           the charging control circuit                                     76           the capacitor                                                    77           the voltage detection circuit                                    81           the commercial AC power supply                                   82           the transformer/rectifier circuit                                83           the constant current circuit                                     84           the constant voltage circuit                                     85           the secondary battery (lithium ion battery)                      86           the voltage detection circuit                                    87           the control circuit                                              88           the current detection resistor                                   89           the current detection circuit                                    90           the load circuit                                                 101          the commercial AC power supply                                   102          the rectifier circuit                                            103          the primary-side control circuit                                 104          the switching transformer                                        104a         the primary-side winding                                         104b         the secondary-side winding                                       104c         the auxiliary winding                                            105          the diode                                                        106          the capacitor                                                    107          the secondary battery (lithium ion battery)                      108          the voltage detection circuit                                    109          the charging control circuit                                     110          the load circuit                                                 111          the 4.2 V detection circuit                                      112          the 4.1 V detection circuit                                      113          the photocoupler                                                 121          the potential difference detection circuit                       122          the charging control circuit                                     131          the charging control circuit                                     132          the resistor                                                     133          the detection circuit                                            141          the charging control circuit                                     151          the resistor                                                     152          the transistor                                                   153, 154     the resistors                                                    155          the detection circuits                                           156          the charging control circuit                                     161          the diode                                                        162          the capacitor                                                    163          the transistor                                                   164          the Zener diode                                                  165, 166     the resistors                                                    167          the detection circuit                                            168          the charging control circuit                                     171          the constant current circuit                                     172          the charging control circuit                                     SW1, SW2, SW3, SW4                                                                         the connection switches                                          SW12         the changeover switch                                            SW13         the connection switch                                            ______________________________________                                    

What is claimed is:
 1. A charging method for a secondary battery,comprising:detecting a charging current; changing over a voltage appliedto said secondary battery to a second voltage lower than a first voltagewhen said charging current reaches a first charging currentcorresponding to a substantially charged condition of said secondarybattery during charging while said first voltage is applied to saidsecondary battery; and changing over said voltage applied to saidsecondary battery to said first voltage when said charging currentexceeds a second charging current corresponding to a discharging batteryvoltage while said second voltage is applied to said secondary battery.2. The charging method according to claim 1, wherein said secondcharging current is equal to said first charging current.
 3. Thecharging method according to claim 1, further comprising:measuring oneof an internal temperature and an environmental temperature surroundingsaid secondary battery; and changing over the application of said secondvoltage to the application of a third voltage instead of said firstvoltage when said measured temperature exceeds a specified temperature,wherein said third voltage is in a range between said first and secondvoltages.
 4. The charging method according to claim 3, wherein saidthird voltage is continuously changed in response to said measuredtemperature.
 5. A charging method for a secondary battery,comprising:detecting a charging current; changing over a voltage appliedto said secondary battery to a second voltage lower than a first voltagewhen a voltage of said secondary battery corresponding to asubstantially charged condition is detected during charging saidsecondary battery while applying said first voltage; and changing oversaid voltage applied to said secondary battery to said first voltagewhen said charging current reaches a specified charging current whilesaid second voltage is applied to said secondary battery.
 6. Thecharging method according to claim 5, further comprising changing overthe application of said second voltage to the application of a thirdvoltage in a range between said first and second voltages instead ofsaid first voltage when one of an internal temperature and anenvironmental temperature surrounding said secondary battery reaches aspecified temperature or higher.
 7. The charging method according toclaim 6, wherein said third voltage is continuously changed in responseto said detected temperature.
 8. A charging method for a secondarybattery, comprising:detecting a potential across respective ends of aswitching means for controlling a supply of a charging power supply tosaid secondary battery and a potential across respective ends of saidsecondary battery while a low-voltage charging power supply is fed tosaid secondary battery; and turning on said switching means based onsaid detected potentials for starting charging of said secondary batterywith said supply of said charging power supply being fed to saidsecondary battery at a specified voltage.
 9. The charging methodaccording to claim 8, wherein a field effect transistor is used as saidswitching means to increase an impedance across respective ends of saidfield effect transistor and for detecting said potential.
 10. Thecharging method according to claim 8, wherein a voltage of said chargingpower supply when detecting said potential is set to a value of aboutthe lowest required voltage for controlling said switching means. 11.The charging method according to the claim 8, wherein said supply ofsaid charging power supply is increased in response to with an increaseof said potential across said respective ends of said secondary batteryafter the start of said charging.
 12. The charging method according toclaim 8, wherein said supply of said charging power supply is changed ina plurality of stages and increased in response to an increase of saidpotential across said respective ends of said secondary battery aftersaid charging begins.
 13. The charging method according to claim 8,wherein said supply of said charging power supply when said potential isdetected is lowered to a voltage below the minimum required forcontrolling said switching means, andsaid charging power supply isaccumulated in a charge-storage means, thereby securing a chargerequired for carrying out a corresponding control by said switchingmeans.
 14. The charging method according to claim 8, wherein aftercharging is stopped when a substantially fully charged state of saidsecondary battery is detected and when said secondary battery isdetected to be at a specified electrical state,charging of saidsecondary battery is restarted after a specified time passes from thisdetection.
 15. The charging method according to claim 14, wherein saidspecified electrical state is detected by detecting that a batteryvoltage of said secondary battery is lower by a specified value than astandard voltage with which said charging voltage is set.
 16. Thecharging method according to claim 14, wherein said specified electricalstate is detected by detecting that a battery voltage reaches aspecified voltage from a voltage value with a grounding potential ofsaid secondary battery set as a standard.
 17. The charging methodaccording to claim 14, wherein said specified electrical state isdetected by detecting that a charging current reaches a specified valuewhen a predetermined voltage is applied to said secondary battery. 18.The charging method according to claim 17, wherein said predeterminedvoltage is a voltage lower than said supply of said charging powersupply.
 19. The charging method according to claim 8, furthercomprising:detecting an electrical condition of said secondary batteryperiodically when a specified time passes from a time when asubstantially fully charged state of said secondary battery is detectedand charging is stopped; and restarting said charging when said detectedelectrical condition is a specified condition.
 20. The charging methodaccording to claim 19, wherein charging is restarted after saidspecified time passes from a time when said specified electricalcondition is detected.
 21. The charging method according to claim 19,wherein said specified condition is a charging current exceeding aspecified value when a charging voltage or a voltage lower than saidcharging voltage is applied to said secondary battery.
 22. The chargingmethod according to claim 19, wherein said specified condition isdetected when a voltage of said secondary battery equals said specifiedvoltage.
 23. The charging method according to claim 22, wherein whensaid voltage of said secondary battery does not reach said specifiedvoltage and charging is not restarted, an energy required for detectingsaid voltage is charged in said secondary battery.
 24. The chargingmethod according to claim 22, wherein said specified condition isdetected when a battery voltage is lower than a specified voltage. 25.The charging method according to claim 22, wherein said specifiedcondition is detected when a battery voltage equals said specifiedvoltage value from a voltage set with a grounding potential of saidsecondary battery designated as a standard.
 26. A charging equipment fora secondary battery, comprising:first voltage feeding means for feedinga first voltage to said secondary battery; second voltage feeding meansfor feeding a second voltage lower than said first voltage to saidsecondary battery; current detection means for detecting a chargingcurrent to said secondary battery; and control means for changing oversaid first voltage feeding means to said second voltage feeding meansbased on an output of said current detection means, wherein when saidcurrent detecting means detects a first charging current correspondingto a substantially charged condition of said secondary battery saidfirst voltage feeding means is changed over to said second voltagefeeding means, and when said current detection means detects a currentexceeding a second charging current while said second voltage feedingmeans is applied, said second voltage feeding means is changed over tosaid first voltage feeding means.
 27. The charging equipment accordingto claim 26, wherein said first charging current is equal to said secondcharging current.
 28. The charging equipment according to claim 26,further comprising:third voltage feeding means for feeding a thirdvoltage in a range between said first and second voltages to saidsecondary battery; and temperature detection means for detecting one ofan internal temperature and an environmental temperature surroundingsaid secondary battery, wherein when said detected temperature exceeds aspecified temperature said second voltage feeding means is changed overto said third voltage feeding means instead of said first voltagefeeding means.
 29. The charging equipment according to claim 28, whereinan output voltage of said third voltage feeding means is continuouslychanged in response to said detected temperature.
 30. A chargingequipment for a secondary battery, comprising;first voltage feedingmeans for feeding a first voltage to said secondary battery; secondvoltage feeding means for feeding a second voltage lower than said firstvoltage to said secondary battery; current detection means for detectinga charging current to said secondary battery; voltage detection meansfor detecting a secondary battery voltage; and control means forchanging over said first voltage feeding means to said second voltagefeeding means based on outputs of said voltage and current detectionmeans, wherein when a specified voltage corresponding to a substantiallycharged condition of said secondary battery is detected by the voltagedetection means said first voltage feeding means is changed over to saidsecond voltage feeding means, and when said current detection meansdetects a current exceeding a specified charging current while saidsecond voltage feeding means is applied to said secondary battery saidsecond voltage feeding means is changed over to said first voltagefeeding means.
 31. The charging equipment according to claim 30, furthercomprising;third voltage feeding means for feeding a third voltage in arange between said first and second voltages to said secondary battery;and temperature detection means for detecting one of an internaltemperature and an environmental temperature surrounding said secondarybattery, wherein when said detected temperature of said temperaturedetecting means exceeds a specified temperature said second voltagefeeding means is changed over to said third voltage feeding meansinstead of said first voltage feeding means.
 32. The charging equipmentaccording to claim 31, wherein said third output voltage of said thirdvoltage feeding means is continuously changed in response to saidtemperature detected by said temperature detecting means.
 33. A chargingequipment for a secondary battery, comprising:a power supply circuit forfeeding a charging power to said secondary battery; switching means forcontrolling said power supply circuit feed to said secondary battery;detecting means for detecting a potential across respective ends of saidswitching means and a potential across respective ends of said secondarybattery while a low-voltage charging power is fed from said power supplycircuit to said secondary battery; and charging control means forstarting charging of said secondary battery by turning on said switchingmeans in response to said detected potentials by said detection meansand for controlling said power supply circuit to feed a specifiedvoltage to said secondary battery.
 34. The charging equipment accordingto claim 33, wherein a field-effect transistor is used as said switchingmeans, and said potential is detected by the said detection means byincreasing an impedance across respective ends of said field-effecttransistor.
 35. The charging equipment according to claim 33, wherein avoltage of said power supply circuit when detected by said detectionmeans is set to a value of about the lowest voltage required forcontrolling said switching means.
 36. The charging equipment accordingto claim 33, wherein said charging power of said power supply isincreased in response to an increase of said potential across saidrespective ends of said secondary battery after starting said charging.37. The charging equipment according to claim 33, wherein said chargingpower of said power supply circuit is varied in a plurality of stages inresponse to an increase of said potential across said respective ends ofsaid secondary battery after starting said charging.
 38. The chargingequipment according to claim 33, wherein a charged load storage means isconnected across said power supply circuit and said charging controlmeans; andsaid charging power of said power supply circuit detected bysaid detection means is lowered to the minimum power required forcontrolling said switching means.
 39. The charging equipment accordingto claim 33, further comprising:battery condition detecting means fordetecting a condition of said secondary battery; and a timer triggeredby said battery condition detecting means, wherein when a specified timepasses from a start of operation of said timer means said chargingcontrol means starts charging said secondary battery.
 40. The chargingequipment according to claim 39, wherein said condition of saidsecondary battery is a specified voltage.
 41. The charging equipmentaccording to claim 39, wherein said condition of said secondary batteryis a charging current of a specified value when a predetermined voltageis applied to said secondary battery.
 42. The charging equipmentaccording to claim 41, wherein said predetermined voltage forpre-charging is a voltage lower than said charging voltage.
 43. Thecharging equipment according to claim 39,wherein said timer means istriggered when said battery condition detection means detects asubstantially fully charged condition of said secondary battery, andsaid charging control means controls said battery condition detectionmeans to detect a condition of said secondary battery periodically whena specified time passes from a time when said timer is triggered, andwhen said detected condition is a specified condition charging isrestarted.
 44. The charging equipment according to claim 43, whereincharging is restarted when said specified time passes from a time whensaid specified condition is detected.
 45. The charging equipmentaccording to claim 43, wherein said battery condition detection meansdetects a charging current exceeding a specified value when a chargingvoltage or a voltage lower than said charging voltage is applied to thesaid secondary battery.
 46. The charging equipment according to claim43, wherein said battery condition detection means detects a batteryvoltage of said secondary battery equal to said specified voltage. 47.The charging equipment according to claim 46, wherein an energy requiredfor detecting a battery voltage is charged in said secondary battery bycontrolling said charging control means when said secondary batteryvoltage does not reach said specified voltage and charging is notrestarted.
 48. An integrated circuit for controlling charging of asecondary battery, in which a charging current to said secondary batteryis detected and control is carried out for selectively supplying a firstvoltage and a second voltage lower than said first voltage to saidsecondary battery, whereinwhen said secondary battery is judged to be ata substantially charged condition based on a first value of saiddetected charging current while said first voltage is applied to saidsecondary battery said first voltage is changed over to said secondvoltage, and when said secondary battery is judged to be in adischarging condition based on a second value of said detected chargingcurrent while said second voltage is applied to said secondary battery,said second voltage is changed over to said first voltage.
 49. Theintegrated circuit according to claim 48, wherein one of an internaltemperature and an environmental temperature surrounding said secondarybattery is measured, and when said measured temperature exceeds aspecified temperature control is carried out for applying a thirdvoltage in a range between said first voltage and said second voltage tosaid secondary battery.
 50. The integrated circuit according to claim48, wherein said third voltage is controlled to be continuously changedin response to said measured temperature.
 51. An integrated circuit forcontrolling charging of a secondary battery, in which a charging currentto said secondary battery is detected and control is carried out forselectively supplying a first voltage and a second voltage lower thansaid first voltage to said secondary battery, whereinwhen said secondarybatter is judged to be at a substantially charged condition based on avalue of a detected charging voltage while said first voltage is appliedto said secondary battery said first voltage is changed over to saidsecond voltage, and when said secondary battery is judged to be in adischarging condition based on a value of said detected charging currentwhile said second voltage is applied to said secondary battery, saidsecond voltage is changed over to said first voltage.
 52. The integratedcircuit according to claim 51, wherein one of an internal temperatureand an environmental temperature surrounding said secondary battery ismeasured, and when said measured temperature exceeds a specifiedtemperature control is carried out for applying a third voltage in arange between said first voltage and said second voltage to saidsecondary battery.
 53. The integrated circuit according to claim 52,wherein said third voltage is controlled to be continuously changed inresponse to said measured temperature.
 54. An integrated circuit forcontrolling charging of a secondary battery, whereina potential acrossrespective ends of a switching means for controlling a supply of acharging power supply to said secondary battery and a potential acrossrespective ends of said secondary battery is detected while alow-voltage charging power supply is fed to said secondary battery, andsaid switching means is controlled based on said detected potentials forstarting charging of said secondary battery with said supply of saidcharging power supply supplied being fed to said secondary battery at aspecified voltage.
 55. The integrated circuit according to claim 54,wherein said detected potential across respective ends of said secondarybattery is judged after said charging begins, andcontrols is carried outto raise said supply of said charging power supply in response to anincrease of said judged potential.
 56. The integrated circuit accordingto claim 54, wherein a detected value of said potential across saidrespective ends of said secondary battery is judged after said chargingbegins, andcontrol is carried out for raising said supply of saidcharging power supply by varying said supply in a plurality of stages inresponse to an increase of said judged potential.
 57. The integratedcircuit according to claim 54, whereinwhen it is judged that the batteryis at a specified electrical condition and after charging is stoppedwhen a substantially fully charged state of said secondary battery isdetected, charging of said secondary battery is restarted after aspecified time passes from the judgment of said specified electricalcondition.
 58. The integrated circuit according to claim 57, whereinsaid specified electrical condition is judged by judging that a batteryvoltage of said secondary battery reaches a specified voltage.
 59. Theintegrated circuit according to claim 57, wherein said specifiedelectrical condition is judged by judging that a charging currentreaches a specified current value when a specified voltage is applied tosaid secondary battery.
 60. The integrated circuit according to claim59, wherein said specified voltage is lower than said supply of saidcharging power supply.
 61. The integrated circuit according to claim 54,whereina specified electrical condition of said secondary battery isjudged periodically when a specified time passes from a time when asubstantially fully charged state of said secondary battery is detectedand charging is stopped, and when it is judged that said battery enterssaid specified electrical condition said charging is restarted.
 62. Theintegrated circuit to claim 61, wherein charging is restarted after saidspecified time passes from a time when it is judged that said specifiedelectrical condition is reached.
 63. The integrated circuit according toclaim 61, wherein said specified electrical condition is a detectedcharging current exceeding a specified value when a charging voltage ora voltage lower than said charging voltage is applied to said secondarybattery.
 64. The integrated circuit according to claim 61, wherein saidspecified electrical condition is a detected secondary battery voltageequal to said specified voltage.
 65. The integrated circuit according toclaim 64, wherein control is carried out so that at least an energyrequired for detecting a battery voltage is charged in said secondarybattery when said detected secondary battery voltage does not reach saidspecified voltage and charging is not restarted.